Model 1311XR Installation and Operation Manual

Transcription

1 GE Measurement & Control Moisture Model 1311XR Installation and Operation Manual A Rev. C November 2015

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3 Model 1311XR General Eastern Chilled Mirror Hygrometer Installation and Operation Manual A Rev. C November General Electric Company. All rights reserved. Technical content subject to change without notice.

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5 Contents Chapter 1. Features and Capabilities 1.1 Introduction Theory of Operation Optical Condensation Hygrometry Hygrometer Function Chapter 2. Installation 2.1 Mounting Location Electrical Connections Gas Sampling Lines Tubing Material and Fitting Measuring Low Frost Points Measuring High Dew Points Filtering the Sample Gas System Coolant Coolant Choice Coolant Temperature Coolant Flow Rate Designing a Calibration Bench for Multiple Sensors DPG-300 Flowmeter Settings Other Flowmeter Settings Chapter 3. Sensor Operation 3.1 Introduction Manual Control Settings Setting the RANGE Switch Setting the FPLL Switch Indicator Lights The 3rd STAGE POWER LED The 4th STAGE POWER LED Heat Pump Controller Error Indicators Operating the Sensor at High Relative Humidity Gas Flow Rate Flow Rate at Very Low Frost Points Purging the Sensor Obtaining Low-Dew-Point Gas for Purging Using a Dryer Using Liquid Nitrogen Sensor Balance Procedure Operating with a Coolant Chiller Avoiding Condensation Model 1311XR Installation and Operation Manual iii

6 Contents 3.11 Helpful Hints Response Time Supercooled Dew Points between 0 and 20 C Measuring Low Frost Points Measurements Above 0 C Mirror Flooding Pressure Effects Chapter 4. Maintenance 4.1 Contamination Mirror Cleanliness Particulate Contaminants Water-Soluble Contaminants Gaseous Contaminants Minimizing the Effects of Contaminants Sample-Line Maintenance Minor Maintenance of Sensor Optics Cleaning the Sensor Mirror Chapter 5. Troubleshooting 5.1 Testing the Sensor s Coolers Fifth-Stage Cooler Test Lower Limit Cooling Test Troubleshooting the 1311XR Power Supply Troubleshooting the 1311XR Power Supply (cont.) S Appears on the STATUS Display Incorrect Dew-Point Display P Remains Illuminated on the Front Panel Appendix A. Specifications A.1 Performance Specifications A.2 Physical Specifications A.3 Accessories iv Model 1311XR Installation and Operation Manual

7 Preface Information Paragraphs Note: These paragraphs provide information that provides a deeper understanding of the situation, but is not essential to the proper completion of the instructions. IMPORTANT: These paragraphs provide information that emphasizes instructions that are essential to proper setup of the equipment. Failure to follow these instructions carefully may cause unreliable performance. CAUTION! This symbol indicates a risk of potential minor personal injury and/or severe damage to the equipment, unless these instructions are followed carefully. WARNING! This symbol indicates a risk of potential serious personal injury, unless these instructions are followed carefully. Safety Issues WARNING! It is the responsibility of the user to make sure all local, county, state and national codes, regulations, rules and laws related to safety and safe operating conditions are met for each installation. Auxiliary Equipment Local Safety Standards The user must make sure that he operates all auxiliary equipment in accordance with local codes, standards, regulations, or laws applicable to safety. Working Area WARNING! Make sure that power to the auxiliary equipment is turned OFF and locked out before you perform maintenance procedures on the equipment. Qualification of Personnel Make sure that all personnel have manufacturer-approved training applicable to the auxiliary equipment. Personal Safety Equipment Make sure that operators and maintenance personnel have all safety equipment applicable to the auxiliary equipment. Examples include safety glasses, protective headgear, safety shoes, etc. Unauthorized Operation Make sure that unauthorized personnel cannot gain access to the operation of the equipment. Model 1311XR Installation and Operation Manual v

8 Preface Environmental Compliance Waste Electrical and Electronic Equipment (WEEE) Directive GE Measurement & Control is an active participant in Europe s Waste Electrical and Electronic Equipment (WEEE) take-back initiative, directive 2012/19/EU. The equipment that you bought has required the extraction and use of natural resources for its production. It may contain hazardous substances that could impact health and the environment. In order to avoid the dissemination of those substances in our environment and to diminish the pressure on the natural resources, we encourage you to use the appropriate take-back systems. Those systems will reuse or recycle most of the materials of your end life equipment in a sound way. The crossed-out wheeled bin symbol invites you to use those systems. If you need more information on the collection, reuse and recycling systems, please contact your local or regional waste administration. Visit for take-back instructions and more information about this initiative. vi Model 1311XR Installation and Operation Manual

9 Chapter 1. Features and Capabilities Chapter 1. Features and Capabilities 1.1 Introduction The 1311XR, a GE top-of-the-line sensor, is a stainless steel, water-cooled, five-stage device that can measure frost points as low as 80 C. Mated with an appropriate M-series or E-series monitor, the system provides state-of the-art frost point measurement at an affordable price. The 1311XR is designed to measure ultra-low frost points. It provides up to 112 C depression capability, enabling humidity measurements below 500ppb. Note: Depression refers to how far the sensor mirror can be cooled below the ambient coolant temperature. The complete sensor includes a Model 1311XR power supply, a Model 1311 heat pump controller, and a 1311XR dew/frost point sensor. The dimensions and layout of the 1311XR are shown in Figure 1 on page 2 and Figure 2 on page 3. The unit s features include: Primary, fundamental measurement of dew/frost point Hermetically sealed, wire-wound, four-wire PRT (Platinum Resistance Thermometer) NIST traceability Interchangeability with other GE sensors without recalibration Continuous, on-line measurement Infrared optics Field-replaceable mirror Liquid cooling Model 1311XR Installation and Operation Manual 1

10 Chapter 1. Features and Capabilities 1.1 Overview (cont.) Figure 1: Model 1311XR Mounting Dimensions and Layout - Front View 2 Model 1311XR Installation and Operation Manual

11 Chapter 1. Features and Capabilities 1.1 Overview (cont.) Figure 2: Model 1311XR Layout - Rear View 1.2 Theory of Operation Optical Condensation Hygrometry Optical condensation hygrometry is a precise technique for determining the water-vapor content of gases by directly measuring the dew or frost point. Using this technique, a metallic mirror is cooled to a temperature at which a thin layer of condensation forms on the surface. The dew layer is detected optically, and a servo loop maintains the mirror temperature at the dew or frost point of the sample gas. Mirror temperature, measured with a platinum resistance thermometer, is an accurate indicator of the dew or frost point. Many of the world s national metrology laboratories use this technique as their standard for accurate, reliable humidity measurement. Model 1311XR Installation and Operation Manual 3

12 Chapter 1. Features and Capabilities Hygrometer Function Figure 3 below illustrates how GE hygrometers detect and measure dew point. The condensate mirror is illuminated with a high-intensity, solid state, light emitting diode (LED). A photodetector measures the intensity of light reflected from the mirror. When the mirror is clear of dew, the photodetector is fully illuminated. As dew forms on the mirror, it receives less light. A separate LED and photodetector pair are used as a known reference to compensate for any thermally induced changes in the optical components. The two photodetectors are arranged in an electrical bridge circuit, the output current of which is proportional to the light reflected from the mirror. The bridge output controls the electrical current to the thermoelectric cooler. A large bridge current develops when the mirror is dry, causing the mirror to cool toward the dew point. As dew forms on the mirror, less light is reflected, and bridge output decreases. This, in turn, causes a decrease in cooling current. A rate feedback loop within the amplifier ensures critical response, causing the mirror to quickly stabilize at a temperature that maintains a thin dew or frost layer on its surface. A precision thermometer embedded within the mirror directly monitors this dew-point temperature. Optical Reference Balance Adjustment Gain Sample Gas LED Regulation Thermoelectric Heat Pump Power 41.2 F Dew Point Temperature (Precision Thermometer) Figure 3: The Chilled-Mirror Hygrometer 4 Model 1311XR Installation and Operation Manual

13 Chapter 2. Installation Chapter 2. Installation 2.1 Mounting Location When selecting a location for the sensor, consider these criteria: Locate the sensor as close as practical to the source of sample gas, to minimize system response time and reduce error at low frost points caused by line outgassing. Choose a sensor location that provides easy access to the dew point chamber cover, to facilitate mirror cleaning. Never operate the sensor in a location where temperatures rise above its maximum rated temperature. 2.2 Electrical Connections Each electrical connector on the Model 1311XR sensor is different from the others, and the cables supplied with the sensor can interconnect the system in only one way. Connect the cables as follows: 1. Plug the instrument into a 115 VAC power outlet. 2. Connect the 37-pin round black connector on the monitor to the 19-pin military-style connector on the back of the 1311XR sensor. 3. Connect the 17-pin military-style connector on the back of the sensor to the 24-pin round connector on the back of the heat pump controller. 4. Connect the nine-pin round connector on the back of the heat pump controller to the eight-pin rectangular connector on the back of the fourth-stage heat pump power supply. 5. Plug the heat-pump power supply into a 115 VAC outlet. Note: To operate the sensor on a voltage other than 115 VAC, order a special unit from GE. Model 1311XR Installation and Operation Manual 5

14 Chapter 2. Installation 2.3 Gas Sampling Lines The sampling system should be designed to allow periodic cleaning. Cleanliness is particularly important at very low humidities, because even a trace of contamination can alter the measured frost point. You may wish to install a tee and closing valve on the inlet side, so the sensor can be shut off while the sampling lines are flushed Tubing Material and Fitting The material used for the gas inlet lines can affect the validity of the readings. Do not use rubber hose or plastic tubing, such as PVC or Tygon, since these materials can absorb moisture. Passivated stainless-steel tubing is strongly recommended. The 1311XR sensor uses ¼-inch stainless-steel compression fittings for the sample gas inlet and outlet at the back of the sensor chassis. Note: The length of the sample tubing between the source and the sensor should be as short as is practical, for quick response and highest accuracy Measuring Low Frost Points When measuring frost points below 30 C, vent sample gas leaving the sensor outlet through an additional line, three to six feet (one to two meters) long, since backflow of ambient moisture into the sensor can occur even under positive pressure, altering the measured frost point. Use passivated stainless-steel tubing and fittings, and ensure that all plumbing is completely free from leaks. At dew/frost points above 20 C, tubing material is not as critical. Impolene, Teflon, polypropylene, aluminum, or brass tubing and fittings may be used Measuring High Dew Points At high temperatures, use stainless steel tubing. If the dew point of the gas is higher that the ambient temperature of the sampling lines carrying gas to the sensor, the lines must be insulated and heated. Heated sample lines may be purchased from the factory, or built from available materials. The simplest way to make heated lines is to wrap heater tape around the tubing. To maintain the desired temperature, the tape may be controlled thermostatically, or it may operate continuously if its wattage is chosen to provide the required temperature rise. Make sure the insulation is adequate to avoid hot and cold sections in the line, and to avoid water condensation/evaporation cycling if the heater is thermostatically controlled. 2.4 Filtering the Sample Gas If the gas to be monitored is free from particulates and hydrocarbon liquids or vapor, filtering is not necessary. Most sample gas streams, however, contain some particulates, and using a filter reduces the need for frequent mirror cleaning. On the other hand, filtering tends to slow the system s response, particularly at low frost points. 6 Model 1311XR Installation and Operation Manual

15 Chapter 2. Installation 2.5 System Coolant The 1311XR sensor must be operated with liquid coolant. Consider the type of coolant, as well as coolant temperature and flow rate Coolant Choice Water, glycol and other noncorrosive liquids are suitable coolants. The coolant can be a recirculated chilled liquid, or tap water that is cooled or chilled, if necessary. If a recirculating chiller is used, it should have a capacity of at least 600 watts at the coolant temperature. See Operating with a Coolant Chiller on page 16 for more information on using chillers Coolant Temperature The maximum permissible coolant temperature is 50 C; the minimum is 2 C. Coolant temperature affects the minimum frost point temperature that can be measured, as shown in Table 1 below. For example, coolant temperature should be kept below 15 C to measure a frost point at 80 C. Temperature of Coolant Water Table 1: Minimum Frost Point Typical Minimum Frost Point Measurement (±3 C) 2 C 85 C 5 C 84 C 10 C 81 C 15 C 80 C 20 C 77 C 25 C 74 C 30 C 70 C 35 C 64 C Connect the coolant lines to the two 3/8-inch brass compression fittings on the back of the 1311XR sensor. Do not operate the sensor without sufficient coolant flow. IMPORTANT: The coolant temperature should not change by more than 0.5 C within any half-hour period. Excessive variation in coolant temperature can cause instability in the system temperature-control loop Coolant Flow Rate A minimum coolant flow rate of 0.1 gallons (0.375 liters) per minute must be maintained for most dew-point measurements. If the fourth-stage power supply control is set below 65 C, the minimum coolant flow rate is 0.25 gallons/minute. Model 1311XR Installation and Operation Manual 7

16 Chapter 2. Installation 2.6 Designing a Calibration Bench for Multiple Sensors When several 1311XR sensors are being operated at low frost points for comparison tests or calibration, GE suggests operating the sensors in parallel, not in series. At low frost points, a series setup may result in delayed response of the downstream sensor. We recommend using series setups only when frost points are above 25 C. Set up the equipment as shown in Figure 4 below. GE recommends using nitrogen as the dry input gas. Dry Gas Inlet HI Low OUTPUT: 10 SCFH If more than four units are in line. DPG-300 Flowmeter Passivated Stainless Steel Tubing Passivated SST Tubing (typ.) Flowmeter NIST Primary Sensor Monitor NIST Primary Passivated SST Tubing (typical) Flowmeter Sensor Monitor System under test #1 Flowmeter Sensor Monitor System under test #2 Flowmeter Sensor Monitor System under test #3 When measuring frost points below -20 C, each sensor outlet should have two to three feet of stainless steel tubing to prevent ambient air backflow into the sensor cavity. Figure 4: Configuration for Calibrating Multiple Sensors 8 Model 1311XR Installation and Operation Manual

17 Chapter 2. Installation DPG-300 Flowmeter Settings The DPG-300 flowmeter controls the total gas flow to the individual sensors and flow meters. Set the DPG-300 flowmeter output to approximately 10 SCFH (4.75 liters/min) if more than four sensors are in use. If you are calibrating many units at a time, adjust the DPG-300 flowmeter as necessary to assure sufficient flow to all flow meters in the line. GE recommends using between three and four feet (0.9 and 1.2 meters) of sample tubing between the DPG-300 and the first parallel flowmeter. If your system requires longer tubing, perhaps 8 to 10 feet (2.5 to 3 meters), between the DPG-300 and the first parallel flowmeter, then the DPG-300 flowmeter setting should be increased Other Flowmeter Settings Maintain the same flow rate on all flow meters. The suggested ranges are shown Table 2 below. Table 2: Gas Flow Rate Dew Point Recommended Flow Rate 10 C 2 SCFH (1 liter/min.) 0 C 2 SCFH (1 liter/min.) 20 to 40 C 1 SCFH (0.5 liter/min.) Below 50 C 3/4 SCFH (0.35 liter/min.) Model 1311XR Installation and Operation Manual 9

18 Chapter 2. Installation [no content intended for this page] 10 Model 1311XR Installation and Operation Manual

19 Chapter 3. Sensor Operation Chapter 3. Sensor Operation 3.1 Introduction Note: This chapter contains complete instructions for operating the sensor. Operation of the complete measurement system is described in the Operator s Manual for the monitor. GE recommends that the 1311XR always be operated with the heat-pump controller RANGE switch set to AUTO and the Frost Point Lower Limit (FPLL) control set to 80 C. With these settings, the system will respond automatically to all dew points within its range (assuming proper configuration of coolant for dew points approaching ambient temperature). The power supply will supply current only as needed. This is the most efficient way to run the 1311XR system. The RANGE switch and the FPLL control are required when the sensor is used with older, manually-controlled monitors, but these functions are handled automatically by M-Series and E-Series monitors. Manual control settings that are primarily useful for troubleshooting are listed in the next section. 3.2 Manual Control Settings Setting the RANGE Switch The RANGE switch on the 1311XR heat pump controller has the settings described in Table 3 below. Setting AUTO Below 55 C 65 C to 10 C Above 25 C Table 3: Manual Control Settings Description When set to AUTO, the system operates automatically, controlling the heat pump in response to any dew or frost point within its operating range. In AUTO mode, the controller senses the current supplied by the monitor to fourth and fifth stages of the thermoelectric cooler. The controller switches on the first through third stages as required to maintain the mirror temperature at the dew/frost point. If the frost point is known to be below 55 C, this setting can be used to provide slightly faster response than the AUTO setting, but depression is limited at this setting. If frost points approaching 80 C are to be measured, always use the AUTO setting. If the frost point is known to be between 65 C and 10 C, this setting can be used to reduce overshoot and settling time. If the dew/frost point is known to be above 25 C, this setting can be used to reduce overshoot and settling time. Note: The AUTO setting is recommended for nearly all applications. It is normal for the third-stage power indicator to blink at any setting. Model 1311XR Installation and Operation Manual 11

20 Chapter 3. Sensor Operation Setting the FPLL Switch The FPLL control on the 1311XR fourth-stage power supply sets the power consumption limit and the coolant requirement when measuring dew/frost points with the range switch set to AUTO, 65 C to 10 C, or BELOW 55 C. If the control is set lower than necessary, the system dissipates excess power, and requires additional cooling to remove the extra heat generated. If the setting is too high, the system may not be able to reach the true dew/frost point. If you set the FPLL to anything other than 80 C, it is better to be conservative and set it for a frost point significantly lower than you expect to measure. The correct setting will cause the 3RD STAGE POWER LED to blink when the system is at the measured frost point. CAUTION! Making changes to the FPLL setting can cause the temperature control loop to become unstable. Example: A system measuring a sample dew point of 40 C was stable with the FPLL set to 80 C, and the heat pump controller RANGE switch set to AUTO. When the FPLL was changed to 50 C, the system was no longer stable or in control. 3.3 Indicator Lights The 3rd STAGE POWER LED The 3RD STAGE POWER LED indicates the power supplied to the fourth and fifth cooling stages of the 1311XR. When the light is OFF, no power is applied to the these stages. When the light is ON steady, full power is being applied. When the 3RD STAGE POWER LED blinks, the 1311XR is in a stable control mode at the dew-point temperature The 4th STAGE POWER LED The 4TH STAGE POWER LED indicates which group of Peltier cooling stages is in operation. When the LED is OFF, the first, second, and/or third cooling stages are operating; if the LED is ON, only the fourth and fifth cooling stages are operating Heat Pump Controller Error Indicators The heat pump controller has two overheat indicators connected to thermal shutdown switches. One indicator monitors the third stage; the other the fourth stage. If the third stage overheat indicator is on, check the cable connections and the coolant flow and temperature. If the fourth stage overheat indicator is on, check the coolant flow and temperature. If either indicator comes on, check for and correct any problems before continuing operation. 3.4 Operating the Sensor at High Relative Humidity The sensor s measurement accuracy may be limited at the upper end of the dew-point range, near saturation, by a margin of stability. At relative humidity values above 85%, small instabilities can cause inconsistent readings. Saturation and loss of stability can be caused by a change of as little as ½ degree in the sensor body temperature. If the dew point is above 90% RH, it may be extremely difficult to obtain a valid reading, and the system is likely to oscillate unless the environment is controlled under strict laboratory conditions. Instability can be reduced by heating the sensor body above the ambient dry-bulb temperature. 12 Model 1311XR Installation and Operation Manual

21 Chapter 3. Sensor Operation 3.5 Gas Flow Rate Although the gas flow rate does not affect the accuracy of dew point sensing, system stability and response time are affected by an inappropriate choice of flow rate. A flow rate of 2 to 2.5 ft 3 /hr (slightly over 1 liter/min) is ideal for most applications. In many cases, flow rates between 0.2 and 5 ft 3 /hr (0.1 and 2.5 liters/min) may be used. Too little flow can slow the response, particularly at very low frost points. Too much flow can cause instability of the control system at high dew points, and can reduce the depression capability of the cooling pump at very low dew points. Too much flow also accelerates the rate of system contamination. The rate of dew or frost layer growth is directly proportional to the rate of sample gas flow. Because the dew growth rate represents a gain/phase term in the mirror temperature-control loop, it affects system stability as well as response time. If the mirror temperature does not stabilize (if it rings or oscillates), the sample flow rate may be too high. 3.6 Flow Rate at Very Low Frost Points At very low frost points, near the limit of mirror temperature depression, the maximum allowable flow rate may be restricted by the depression requirement. As flow rate increases, more heat is carried away from the mirror, reducing the temperature depression. The trade-off is response time versus the low limit of temperature measurement. At low flow rates, an additional limitation is the time required to change the volume of gas in the sampling system so that its frost point is representative of the volume from which the sample is drawn. Further, it takes substantially longer to grow frost than to grow dew because of reduced vapor concentration and crystal growth effects. Developing the required frost layer necessary for control when near maximum temperature depression can take as long as 30 minutes. This time could be shortened by increasing the flow rate, but a higher flow rate may add heat to the mirror faster than it can be pumped away, raising its temperature above the frost point. 3.7 Purging the Sensor CAUTION! The 1311XR must be purged after each use, either with the sample gas after measuring it, or with another dry gas source. Otherwise, condensation inside the sensor housing may cause corrosion and eventual failure of the thermoelectric coolers. When measuring gases having an extremely low frost point, the sensor must be purged after each use with a gas having a frost point lower than 20 C. For higher frost points, use any gas having a frost point at least as low as the sample gas. The sensor s sample-gas outflow is often a good choice for purging. A purging method should be included when planning the installation. Introduce the purge gas through the purge fitting at the rear of the sensor. The simplest method for purging is to run the sample gas outflow through the U-tube supplied with the sensor. Model 1311XR Installation and Operation Manual 13

22 Chapter 3. Sensor Operation 3.8 Obtaining Low-Dew-Point Gas for Purging Using a Dryer To obtain a source of dry gas, GE Infrastructure Sensing previously recommended using a compressor (providing 7 to 10 bar) followed by a dryer and a surge tank. The compressor provides the elevated pressure that allows the dryer to work more efficiently. The surge tank removes the pulses of pressure from the compressor, and allows the compressor to cycle on and off while the dry gas is being drawn off. This method provides the required dried gas, but has the following disadvantages: Expensive components Electricity has significant cost Questionable working of dryer Possible downtime for compressor or dryer service Using Liquid Nitrogen For reasons of simplicity and reliability, GE now recommends using liquid nitrogen for the purge gas. Bottled liquid nitrogen may be purchased in insulated containers from a supplier of industrial gases. The advantages of liquid nitrogen are: The gas boiled off is consistently dry There are no compressor failures or dryer questions The cost of nitrogen compares favorably with the previous cost of electricity Note: The pressure of gas from bottled nitrogen is about 30psi. 14 Model 1311XR Installation and Operation Manual

23 Chapter 3. Sensor Operation 3.9 Sensor Balance Procedure Improper adjustment of the optical balance is the most common cause of instrument malfunction. If the service indicator displays S after a PACER cycle, even after performing the mirror cleaning procedure (described in Cleaning the Sensor Mirror on page 20), check the sensor balance adjustment. In addition, new systems may require an optical balance adjustment after one or two months of operation. The balance procedure is performed as follows: 1. Set the heat pump range switch fully clockwise to the ABOVE 25 C position, and the power supply knob fully clockwise to 55 C. 2. Set the monitor to HEAT mode. 3. Wait for the mirror temperature indicated on the monitor to rise 15 C above the cooling water temperature. CAUTION! If the 1311XR has been operating at frost points below 60 C, wait at least 20 minutes before opening the sensor; otherwise, condensation from the room air is likely to occur. 4. Open the sensor, and clean the mirror. 5. Referring to the operating instructions for the monitor, set the monitor to the sensor balance function. 6. With ambient light blocked from the mirror area, adjust the sensor s balance (bias adjustment) screw to the transition point between no bars lit and one (and only one) bar lit on the monitor s dew thickness display. If no dew-layer thickness bars light, or if two or more bars remain lit, readjust the bias past the transition point, then back up so that only one bar is lit. 7. Close the sensor, and resume the flow of sample gas. The quickest results are achieved with a sample gas having a dew point of about 30 C. Drier gas requires a longer time to reach equilibrium control, and gas with a higher dew point is not representative of the normal operating range of the 1311XR. 8. Return the monitor to the OPERATE mode. Set the RANGE switch on the heat pump controller fully counterclockwise to AUTO. 9. Wait for the monitor s green light to indicate CONTROL. With a sample dew point of 30 C, this will take five to ten minutes. The monitor SERVICE indicator may be on during this time.) Initiate a PACER cycle. At the end of this cycle, the SERVICE indicator will go off, the monitor will display the sample dew point, and the green CONTROL light will illuminate. Note: For most conditions, operate the 1311XR with the FPLL switch to 80 C, and the controller range switch set to AUTO. Model 1311XR Installation and Operation Manual 15

24 Chapter 3. Sensor Operation 3.10 Operating with a Coolant Chiller A recirculating chiller may be used in place of a continuous stream of tap water. The chiller must have a capacity of 600 watts Avoiding Condensation When using a low coolant temperature in an effort to measure low dew points or get fast response time, be careful to never cause condensation inside the sensor. Most chillers can sustain the coolant temperature below the dew point of room air. Here, condensation is an ever-present concern. If purging with the sample gas flowing from the sensor causes condensation, it is helpful to use a dry purge gas, such as dry nitrogen or dried air Helpful Hints Response Time At dew points above 0 C, the system normally stabilizes in a few minutes with a consistent dew or frost layer. The green control light illuminates when the system is stable and valid readings may be taken. When the system is operating at very low frost points (below 40 C), extra care may be required when interpreting readings because of a slower system response. Response depends on a number of factors, including dew/frost point, slew rate, upstream filtering, and the flow rate. As the dew/frost point becomes lower, water molecules in the air sample become scarcer, and it takes longer to condense a frost layer on the mirror that is sufficiently thick to establish an equilibrium condition. Temperature slew rate depends on dew point and depression (the temperature difference between the mirror and the sensor body). At higher dew points and moderate depressions, the slew rate is typically 1.5 C/second. At lower dew points and/or larger depressions, the slew rate becomes progressively slower. Flow rate affects response by determining the rate at which water vapor is supplied to or carried off the mirror. 16 Model 1311XR Installation and Operation Manual

25 Chapter 3. Sensor Operation Response Time (cont.) The user should consider the trade-off between response time, control system stability, and sensitivity to contamination. Table 4 lists response times to a variety of temperature changes. These are the response times required to meet the accuracy specifications of the instrument. Please note that the instrument may come into control before the highest accuracy reading is achieved. Table 4: Sensor Response Response Time Step Change to Step Change +10 to 80 C 360 to 600 min. +10 to 75 C 360 to 600 min. +10 to 65 C 360 to 450 min. 65 to 55 C 30 to 40 min. 55 to 30 C 30 to 40 min. 30 to 10 C 10 to 20 min. 10 to +10 C 40 to 60 min. +10 to 25 C 40 to 60 min. +10 to 30 C 40 to 60 min. 30 to 20 C 20 to 30 min. 20 to 10 C 20 to 30 min. 10 to 0 C 15 to 20 min. 0 to +10 C 15 to 20 min. +10 to +25 C 15 to 20 min. +10 to 10 C 20 to 30 min Supercooled Dew Points between 0 and 20 C Between 0 C and 20 C, water can exist in a supercooled liquid state for extended periods of time. Extra care may be needed when making measurements in this temperature range, because the mirror may temporarily stabilize at the supercooled dew point, 0.5 to 1 C below the actual frost point. To assure that the unit is operating in the ice phase within this temperature range, allow the sensor to operate continuously at 30 C for one or two hours to grow a uniform frost layer. Then, the system is ready to accurately measure higher frost points. Model 1311XR Installation and Operation Manual 17

26 Chapter 3. Sensor Operation Measuring Low Frost Points When measuring dew points below 50 C immediately followed by dew points above 30 C, use the following procedure: 1. Turn the unit off. 2. Wait at least 45 minutes for the temperature of the coolers to stabilize at ambient room temperature. 3. Turn the unit on, and make the desired measurement at the higher dew point Measurements Above 0 C For dew points above 0 C, observe the following precautions: Coolant water must be at least 10 C above the dew point at all times. The heat pump controller switch should be set to ABOVE 25 C, and the FPLL control should be set to 60 C. Setting the FPLL control to 50 C turns off the power supply completely, and may lead to overheating, since the coolers will not operate. If condensation remains a problem with dew points above 0 C, inject dry nitrogen gas at a rate of 1 SCFH (0.5 liter/min) into the OUTLET connection at the rear of the 1311XR Mirror Flooding An abrupt transition from dry to moist conditions (particularly when accompanied by a transition from cold to warm temperatures) may cause the mirror to accumulate an overload of moisture. The sensor may require many minutes to dry out before valid readings can be obtained. The drying process can be accelerated by setting the monitor s SENSOR switch to HEAT, which temporarily warms the sensor Pressure Effects The sensor location and hookup arrangement can influence the pressure to which the sensor chamber is exposed. If the pressure of the gas changes, the dew point correspondingly changes even though the mixing ratio (moisture content) stays constant. The monitor, of course, displays the dew/frost point at the sensor, and any pressure drop in the sensor lines can affect the measurement. The dew-point change caused by pressure changes can be calculated by using Dalton s Law and the Smithsonian Tables, or a proper nomograph. 18 Model 1311XR Installation and Operation Manual

27 Chapter 4. Maintenance Chapter 4. Maintenance 4.1 Contamination Mirror Cleanliness Proper operation of a condensation hygrometer depends on the condition of the mirror surface. In general, accuracy is reduced when contaminants accumulate on the mirror. However, the mirror does not have to be microscopically clean. In fact, the mirror performs best a few hours after cleaning, when a number of nucleation sites have begun to form. On an unscratched, freshly cleaned mirror, there are relatively few nucleation sites on which dew or frost deposits can form, and, as a result, more time is required to collect a condensation layer at low frost points. In addition, overshoot may occur, which can cause oscillations as the temperature stabilizes Particulate Contaminants Particulate matter that is insoluble in water may accumulate on the mirror surface, but does not affect instrument accuracy until the mirror reflectance is substantially reduced. In many cases, particulates actually improve instrument response by providing condensation sites Water-Soluble Contaminants Contaminants that readily dissolve in water, such as naturally occurring salts, interfere with accurate vapor concentration measurement by any condensation method. These materials readily go into solution with the water condensate on the mirror surface, and reduce the vapor pressure in accordance with Raoult s Law. As the concentration increases with time, the saturation vapor pressure of the liquid solution decreases. The unit responds to this lower vapor pressure by elevating the mirror temperature, which maintains vapor pressure in equilibrium with the partial pressure of atmospheric water vapor; therefore, the displayed dew point drifts upward above the true dew point. Since the measurement error increases gradually, it often goes undetected. To determine whether dissolved contaminants are affecting dew-point measurement, perform the following steps: 1. Note the indicated dew point 2. Clean the mirror 3. Balance the optics by initiating a PACER cycle 4. Measure the dew point again If the new reading is lower than the first reading, soluble material probably was present in sufficient quantity to cause a measurement error Gaseous Contaminants When the sample gas contains a gaseous material that has a condensation temperature higher than that of water, even in very low concentrations, the system will eventually control on that material rather than on water. It then displays the condensation temperature of the contaminant, not water. This material accumulates on the mirror only when chilled; in the normal atmosphere, gaseous contaminants do not have a detectable effect. Model 1311XR Installation and Operation Manual 19

28 Chapter 4. Maintenance Minimizing the Effects of Contaminants To reduce the effects of contamination, use the following techniques: Use the PACER feature to reduce the effect of contaminants on the unit s performance. Reduce the gas flow rate to reduce the rate of contaminant accumulation on the mirror. Clean the mirror according to the recommended optics cleaning procedure (see Cleaning the Sensor Mirror on page 20). To determine the proper cleaning interval for a given set of conditions, take a dew-point reading before and after the cleaning. Any appreciable shift indicates that, under these conditions, the mirror should be cleaned more often. 4.2 Sample-Line Maintenance Contaminated sample lines slow the unit s response time and can cause erroneous readings, usually on the high side. To reduce the rate of contamination, reduce the flow and/or install a filter upstream. Clean the sample lines as often as necessary. To determine the required cleaning frequency, take dew-point readings before and after cleaning the lines, sensor cavity, and mirror. If the two readings differ appreciably, the sampling lines should be cleaned more often. 4.3 Minor Maintenance of Sensor Optics Inspect and maintain the sensor optics periodically as described in the following procedure. This procedure can be performed any time, but is only necessary when the letter S appears on the status display, indicating that service is required. 4.4 Cleaning the Sensor Mirror Under normal conditions, the system is self-checking and self-balancing. However, there are occasions when particulate matter and water-soluble contaminants reduce sensor-mirror reflectance and system accuracy (see Contamination on page 19). When necessary, clean the sensor mirror, using the following procedure: 1. Deactivate the sensor cooler, using one of the following actions: Turn the power off or move the sensor switch to heat or disconnect the sensor cable 2. Turn off the sample gas. IMPORTANT: Be sure the sensor cavity is depressurized before continuing with the next step. 3. Open the sensor by removing the sensor cover. 4. Moisten a cotton swab with a cleaning solution suitable for mirrors, such as the blue cleaning solution in the maintenance kit, or dilute methanol or ethanol. Clean the mirror with a few light wipes. If the sensor is significantly contaminated, clean the other optical surfaces in the sensor as well as the sensor cavity itself. 5. Replace the sensor cover. 6. Return all switches to their normal positions, initiate a PACER cycle, and continue operation. 20 Model 1311XR Installation and Operation Manual

29 Chapter 5. Troubleshooting Chapter 5. Troubleshooting 5.1 Testing the Sensor s Coolers Fifth-Stage Cooler Test Perform the following test with: A dry gas source connected to the sensor Dry gas purging the sensor enclosure Connector J9 (the cooler drive) disconnected from the monitor. (J9 has larger diameter wires than other connectors.) 1. Set the heat pump controller RANGE switch fully clockwise to ABOVE 25 C, its highest limit. 2. Set the FPLL control fully clockwise to 55 C. 3. Initiate a PACER cycle; when complete, the monitor will read the ambient temperature. 4. Set the FPLL control counterclockwise to 80 C, its lowest limit. 5. Set the RANGE switch to the 10 TO 65 C position. The dew point displayed on the monitor will begin going down to approximately 10 C. Wait until it stabilizes. 6. Set the RANGE switch to the BELOW 55 C position. The displayed dew point should go down further, to approximately 40 C. If the 1311XR responds properly to this test, its fifth-stage cooler is working. If it does not meet the specification, check the following: Make sure the power supply is plugged in and the fan is running. Check the 15-amp fuse. Make sure that the cable connecting the power supply to the controller is in place. If any of these results is not obtained, please contact GE for assistance. If there is insufficient cooling or no cooling, the fifth stage may have failed, and the sensor may need to be returned to GE for repair. 7. When you have competed the test, replace connector J9 on the monitor. Model 1311XR Installation and Operation Manual 21

30 Chapter 5. Troubleshooting Lower Limit Cooling Test To determine whether or not the 1311XR is cooling to its lower limit, perform the following procedure: 1. Connect a source of dry gas to the 1311XR. 2. Remove the cooler fuse from the rear of the power supply, to interrupt power to the fifth-stage cooler. 3. Inspect this fuse to confirm that it will provide continuity when installed. 4. Operate the 1311XR. The dew point displayed on the monitor should fall to about 38 C to 40 C when using 15 C cooling water. Obtaining this minimum mirror temperature confirms that the top section of the 1311XR is functioning properly. If the cooling water is colder, a somewhat lower minimum mirror temperature will be reached. Record the minimum temperature obtained. 5. If the 1311XR cannot cool to 38 C with the fifth stage disconnected, check to see whether the sensor or instrument is the source of the problem by operating the 1311XR with a different monitor. 6. Re-install the cooler fuse. Set the RANGE switch to AUTO. Set the FPLL control to 80 C. 7. Operate the 1311XR. The mirror temperature should now fall to about 80 C. 5.2 Troubleshooting the 1311XR Power Supply If the power supply does not operate properly, check the following: Note: 1. Are the cables connected? 2. Is the 1311XR receiving line power? The sensor design requires line power from two sources: the normal line cord and the monitor. GE standard monitors do not supply line power through the sensor connector. Monitors modified for the 1311XR, as well as those manufactured prior to April 1992, have pin 1 of the sensor connector wired to neutral, and pin 2 wired to the hot side of AC power. For M1 monitors manufactured before September 1993 (with the transformer mounted on the PC board) which do not have AC line power wired to pins 1 and 2 of the sensor connector, AC power may be accessed from J10, pins 11 and 12. For an M1 monitor manufactured after September 1993 (with the transformer chassis-mounted) or a later M Series or E Series monitor, consider connecting two wires from the transformer primary to pin 1 and pin 2. Line power on the sensor connector should be fused and switched. 3. Line power is supplied from the monitor through the 1311XRK cable on pins 23 and 24 of the sensor cable. Measure the voltage at these pins to confirm that line power is reaching the sensor. 22 Model 1311XR Installation and Operation Manual

31 Chapter 5. Troubleshooting 5.3 Troubleshooting the 1311XR Power Supply (cont.) Note: 4. Check the sensor controls and indicators: a. Is the RANGE switch set to AUTO? b. Is the FPLL control set to 80 C? c. Is the controller system power light (D1) on? This is required for operation. d. Is the third-stage power light (D5) on? The status of the fourth-stage power light (D4) is irrelevant. 5. Are both fuses (F1 & F2) installed and functioning? Check for power on each side of the fuses. 6. Is the fan running? 7. Can 12 VDC be measured across pins 5 and 8 of J2 or pins 3 and 4 of the solid-state relay? If not, check the connections, and begin troubleshooting the controller. 8. Is AC power available at pins 1 and 2 at the base of the solid-state relay? If the solid-state relay has failed, it can be changed in the field. 9. Is AC power reaching the large, 3 Ohm, 100-watt resistor? The connection of the wires to this resistor occasionally fails. 10. Is the AC voltage between pins 1 and 3 of the variable transformer between 20 and 50 VAC (depending on the rotor position)? 11. Is the voltage across the large capacitor 80 VDC? 5.4 S Appears on the STATUS Display The letter S displayed on the monitor s STATUS readout indicates that service is required. The most frequent problem is mirror surface contamination that requires cleaning, as follows: 1. Clean the sensor mirror (see Cleaning the Sensor Mirror on page 20). 2. Run the instrument through a PACER cycle. 3. If S appears again at the end of the cycle, balance the sensor optics (see Sensor Balance Procedure on page 15). Model 1311XR Installation and Operation Manual 23