Product Specifications Foxboro Dew Point Measurement System Model 2761 Mechanical DEWCEL Element Model 2781 Electrical DEWCEL Element PSS 1-5A1 A MODEL 2761 MODEL 2781 The Foxboro Dew Point Measurement System provides a direct reading of absolute humidity in ambient temperatures between -45 and +105 C (-50 and +220 F). GENERAL DESCRIPTION A typical system consists of a Foxboro DEWCEL element (moisture-sensitive element), a 25 V ac power source, and a recorder, indicator, transmitter, or controller. The DEWCEL element operates by automatically maintaining a saturated solution of hygroscopic salt at a temperature which is in equilibrium with the vapor pressure of the measured atmosphere. This equilibrium temperature is sensed by a filled thermal system, thermocouple, or resistance temperature detector (RTD), and can be expressed directly in any absolute moisture unit by means of a characterized scale, dial, or chart, or a computer program. The performance of the DEWCEL element is both accurate and stable and is unaffected by ambient temperature changes. RELIABLE OPERATION The Foxboro DEWCEL element was invented and introduced in 1948, and since then it has been accepted throughout the world as one of the most accurate and reliable devices for continuous moisture measurement. From weather services to process plants, the DEWCEL element has provided high integrity moisture measurement for monitoring and control in a variety of environmental and process applications. The operation of the DEWCEL element is based entirely upon the predictable behavior of lithium chloride solution which maintains a vapor pressure equilibrium with the surrounding atmosphere. The DEWCEL element, therefore, requires no adjustment or calibration to ensure specified performance.
Page 2 REPLACEABLE TEMPERATURE SENSOR The DEWCEL element consists of two active parts: a heater electrode assembly, and a temperature sensor. Both the Model 2781 (electrical type) and the Model 2761 (mechanical type) feature easy replacement of the temperature sensor. In addition to significantly reducing maintenance with a variety of receiving devices, the cost of maintenance is further reduced by easy replacement of the heater element (M2781 only). LOW MAINTENANCE The DEWCEL element has proven to be sturdy and dependable. It typically operates well in most environments which may be contaminated with oil traces and particulate matter. In order to achieve optimum performance, the DEWCEL element should be periodically washed with distilled water and resaturated with a 5% (in water by weight) lithium chloride salt solution. Depending upon the application, the operational life of the salt solution may extend up to 15 months. FUNCTIONAL SPECIFICATIONS DEWCEL Element Accuracy ±0.8 C (±1.5 F) at 32 C (90 F) dew point (not including temperature sensor errors). Dew Point Temperature Range Limits -45 and +60 C (-50 and +140 F). Ambient Temperature Range Limits -45 and +105 C (-50 and +220 F) Relative Humidity Limits 12 and 100% relative humidity. Pressure Rating Full vacuum up to 850 kpa (125 psi, 8.5 bar or kg/cm 2 ). Element Leads the Model 2761 has a 3 m (10 ft), 2-conductor cable for connecting the element to the power unit. The Model 2781 has five terminals in the connection head: two for connecting the element to the power unit, and three for connecting the temperature sensor to the receiving device. Supply Voltage Requirements The Model 2740 Power Unit for one DEWCEL element is for 100, 120, 220, or 240 V, 50 or 60 Hz, as specified. Other power units for up to six DEWCEL elements are for 120 V, 60 Hz operation only. Refer to Model Code section. Element Shield (Specified by Model Number) Perforated Tube Type for atmospheric velocities up to 0.3 m/s (1 ft/s). Open End Type for velocities over 0.3 m/s (1 ft/s) up to 5 ms/ (16 ft/s). Mounting MODEL 2761 (1) Has a flange for mounting on the process with 1.000-18 internal thread for the thermal system jam nut. MODEL 2781 (1) The element guard includes a 1 NPT external thread for mounting on the process and 1.250-18 internal thread for the DEWCEL element jam nut. PHYSICAL SPECIFICATIONS Material of Construction FLANGE (MODEL 2781) Brass forging with black paint on external nonprocess-wetted surfaces. CONNECTION HEAD (MODEL 2781) Cast aluminum body and cover with a rubber gasket. The connection head assembly is weatherproof and dusttight as defined in IEC IP65 and provides the environmental protection of NEMA Type 4. JAM NUT (ALL MODELS) Nickel-plated brass TEMPERATURE SENSOR SHEATH AISI Type 316 stainless steel (316 ss) coated with Heresite for electrical insulation. HEATER WIRES 18 or 24 karat gold, as specified by Model Number. ELEMENT SHIELD Nickel-plated brass tube. MODEL 2740 POWER UNIT Sheet steel with textured gray paint, suitable for installation in General Purpose locations. Approximate Size, H x W x D: 260 x 213 x 107 mm (10.3 x 8.4 x 4.2 in) (1) The Model 2761 is designed for a filled thermal system temperature sensor, while the Model 2781 is designed for a thermocouple or RTD sensor. Refer to Model Code section.
(a) Not a direct replacement for instruments prior to 2004. (b) Specify extension cable length. OPTIONAL SELECTIONS PSS 1-5A1 A Page 3 Optional Feature Description Specify Weather Hood Aluminum enclosure with conical top, cylindrical wall, and offset mounting bracket to protect DEWCEL element in outdoor installations. Model 2704 Model 2714 Draft Shield A sheet steel enclosure for use in ducts where the atmospheric velocity exceeds 5 m/s (16 ft/s) but is not over 10 m/s (32 ft/s). Model 2715 Air-Cooled Sampling Chamber Water-Cooled Sampling Chamber Ballast Resistor Perforated Tube Element Shield Open End Tube Element Shield Galvanized sheet steel enclosure used in those applications where the ambient temperature of the measured atmosphere exceeds 105 C (220 F). Specify separate dry-bulb measurement system with sensor code 4442 (Class IA), U = 178 mm (7 in), and 1/2 NPT bushing. Similar to above except, water cooled. Nonilluminating alternate for power unit lamps. Used in areas where vibration would destroy the lamps, 9 Ω, 95 W resistor. For protection and use with flow velocities up to 0.3 m/s (1 ft/s) For protection and use with flow velocities up to 5 m/s (16 ft/s) 100 W, 34 V ballast resistor for Model 2761 DEWCEL Element 50 W, 34 V ballast resistor for Model 2781 DEWCEL Element Replacement Lamp for Power Units Extension Cable 5 conductors with terminals for connection to Model 2781 DEWCEL Element, 3 m (10 ft) long 5 conductors (2 for the element, 3 for measurement) 3 conductors (for measurement) 2 conductors (for the element) Additional DEWCEL Element Solution Customer Tag 30 ml (1 U.S. fl oz) bottle 0.47 L (1 U.S. pint) bottle Stainless steel tag wired to instrument for customer tag data. There can be a maximum of 10 lines of data with 40 characters and spaces per line. Model 2707 Model 2707A Model 2748 Model 2748A Part A089700 (a) Part 0043933 Part 0048955 Part H0103AL Part H0103AM Part 0048189 Part 0048939 Part H0103AP Part R0101BA (b) Part R0101LY (b) Part 0026102 (b) Part 0048192 Part H0103AY AS Code MTS
Page 4 Mechanical DEWCEL Element MODEL CODES 2761 = Mechanical DEWCEL Element (For use with filled thermal system) Heater Winding Material -18 = 18 Karat Gold Wire -24 = 24 Karat Gold Wire C M Element Shield = Perforated Tube [(velocities up to 0.3 m/s (1 ft/s)] = Open End [velocities over 0.3 up to 5 m/s (1 up to 16 ft/s)] Electrode Insulation G = Glass Tape Example: 2761-18CG Electrical DEWCEL Element 2781 = Electrical DEWCEL Element Heater Winding Material -18 = 18 Karat Gold Wire -24 = 24 Karat Gold Wire C = M = Element Shield Perforated Tube [(velocities up to 0.3 m/s (1 ft/s)] Open End [velocities over 0.3 up to 5 m/s (1 up to 16 ft/s)] G = Electrode Insulation Glass Tape Temperature Sensor N = Nickel RTD, NR226 Q = Platinum RTD, DIN 100 Ω at 0 C, PR238 P = Platinum RTD, SAMA 100 Ω nominal, PR278 J = Iron-Constantan Thermocouple K = Chromel-Alumel Thermocouple T = Copper-Constantan Thermocouple W = Without Temperature Sensor Example: 2781-18CGN Power Unit DEWCEL Element Power Unit (a)(b) 2740 = For one Model 2761 or 2781 DEWCEL element (a) For 100, 120, 220, or 240 V ac, 50 or 60 Hz operation. (b) Maximum DEWCEL Element Operating Pressure: 0 Paa to 865 kpag (0 psia to 125 psig).
Page 5 DIMENSIONS NOMINAL mm in MODEL 2761 MECHANICAL DEWCEL ELEMENT 82.6 mm (3.25 in) DIA. TAPPED FOR 1/2 NPT 72 TAPPED FOR 1.000-18 NS-2 7.1 mm (0.28 in) DIA. 5 PLACES 98 3.9 45 10 0.4 45 1.8 238 9.4 45 1.8
Page 6 DIMENSIONS NOMINAL (Cont.) mm in MODEL 2781 MECHANICAL DEWCEL ELEMENT 43 1.7 38 1.5 137 5.4 TAPPED FOR 3/4 NPT CONDUIT FITTING 203 8.0 25 1.0 1 NPT 127 1.1 29 1.1
Page 7 DIMENSIONS NOMINAL (Cont.) mm in MODEL 2715 DRAFT SHIELD 13 0.5 8 HOLES, 6 mm (0.219 in) DIA., FOR 0.187 in BOLTS 102 4.0 229 9.0 102 4.0 13 0.5 89 3.5 102 4.0 203 8.0 UNIT TO BE INSTALLED IN USER'S DUCT DIRECTION OF FLOW C DEWCEL L ELEMENT 127 5.0 1 in NPT 152 6.0 89 3.5 25 1.0 TYPICAL SAMPLING CHAMBER - MODEL 2707A SHOWN PROCESS INLET 1/2 NPT BAFFLE 51 2.0 114 4.5 114 4.5 254 10 1/4 NPT SUCTION OUTLET 51 2.0
Page 8 ORDERING INSTRUCTIONS 1. DEWCEL Element Model Number 2. For Mechanical DEWCEL Elements, provide temperature measuring instrument Model Number and filled thermal system specifications. 3. Power Unit Model Number 4. Optional Selections - see table in Optional Selections section. 5. Tag OTHER M&I PRODUCTS Invensys Process Systems provides a broad range of measurement and instrument products, including solutions for pressure, flow, analytical, positioners, temperature, controlling and recording. For a listing of these offerings, visit the Invensys Process Systems web site at: www.foxboro.com/instrumentation 33 Commercial Street Foxboro, MA 02035-2099 United States of America www.foxboro.com Inside U.S.: 1-866-746-6477 Outside U.S.: 1-508-549-2424 or contact your local Foxboro representative. Facsimile: 1-508-549-4999 Invensys, Foxboro, and DEWCEL are trademarks of Invensys plc, its subsidiaries, and affiliates. All other brand names may be trademarks of their respective owners. Copyright 1985-2008 Invensys Systems, Inc. All rights reserved MB 010 Printed in U.S.A. 0908