TRANSDUCERS. Conversion of Measured Strain or Output Voltage into Physical Quantity. Sensitivity Decrease due to Cable Extension

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Kenneth Miller
6 years ago
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2-2 Strain gage transducers are designed to transduce physical variables such as load, force, pressure, acceleration, vibration, displacement and torque into electric signals by using strain gages as

1 2-2 Strain gage transducers are designed to transduce physical variables such as load, force, pressure, acceleration, vibration, displacement and torque into electric signals by using strain gages as sensing elements. The electric output signals can be connected to various measuring instruments to monitor, record and control physical variables. Use of strain gages as sensing elements makes the transducers compact and lightweight, while ensuring least mechanical displacement and superior linearity due to simple structure. Practically, strain gage transducers are widely used for research and as industrial measuring devices for production control. Among them, load cells are used to detect compressive or tensile force; pressure transducers, to detect water, oil or air pressure; acceleration transducers, to detect impact or vibration acceleration; displacement transducers, to detect displacement in various loading tests and materials tests; torque transducers, to detect torque such as twisting force of a rotating object; transducers for automotive tests; and civil engineering and architectural transducers, to measure soil pressure, stress, pore pressure, etc. Conversion of Measured Strain or Output Voltage into Physical Quantity Measured strain or output voltage can easily be converted into physical quantity by using the calibration coefficient written in the Test Data Sheet attached to each transducer. Measured strain on strain amplifier Wanted physical quantity = Measured strain (μm/m) x A A: Calibration coefficient indicating the physical quantity corresponding to 1-μm/m equivalent strain. Output voltage on other type of amplifier or recorder Wanted physical quantity = Bridge output voltage (μv) Bridge voltage (V) B: Calibration coefficient indicating physical quantity corresponding to 1-μV output/1-v bridge voltage x B Sensitivity Decrease due to Cable Extension If a strain gage transducer is connected to a signal conditioner, digital indicator or strain amplifier via extension cable, we cannot ignore the sensitivity decrease due to the extension cable resistance which lowers the voltage applied to the transducer. The rated output with lowered sensitivity can be obtained through the following equation: ε0 = R εi ( R+( r L) ) R :'s input resistance (Ω) r :Extension cable's reciprocating resistance (Ω) per meter L :Extension cable length (m) εi :Rated output written in Calibration Sheet Relation between Output (mv/v) and Strain Quantity (μm/m) Rated output of each transducer is stated in mv/v. It indicates the voltage (mv) which is output for the rated capacity with the bridge voltage at 1 V. The output voltage has the following relation with a strain quantity (μm/m): 1 mv/v = 2000μm/m For details, refer to Sensitivity Decrease in KYOWA Extension Cables Model N-82 N-83 N-84 N-85 N-100 Cable Length (L) 10m 20m 30m 50m 100m Ratio of Sensitivity Decrease (approx.) 0.2% 0.5% 0.7% 1.1% 2.2% r L (Ω) (approx.) Bridge resistance R = 350Ω, Reciprocating resistance per 1 m of four 0.5 mm 2 -conductor chloroprene cabtyre extension cable = Ω (approx. 0.08Ω) Reference R R+( r L)

2 2-3 Cells ( s) KYOWA load cells offer outstanding and sustained performance over long periods of usage even under harsh operating conditions by adopting our independently developed, dedicated strain gages of excellent accuracy, our superior production technologies, calibration equipment of supreme precision, and our rich experience in this field. We offer a full range of models to satisfy all industrial needs, including models for compression and tension applications; explosion-proof models usable in environments containing dangerously explosive liquids, gases, powders, etc.; washer type models for measuring rolling pressure, etc. KYOWA load cells can be used in sensing applications ranging from general force measurement in testing or research to measuring and controlling weight (mass) in tanks, hoppers, mills, vehicles, etc. Discounted pricing is available to clients placing high-volume orders. Inquiries are welcome. Typical Structure Features Enable highly accurate measurement Stably operate for long periods of usage even under harsh conditions Ensure long service life against repetitive loads Important Notice cells cannot be used under hydrogen environment. To Ensure Safe Usage 1. The rated capacity of each load cell is designed for cases of center spindle loads only. In cases involving inclined loads, angular moment, horizontal force or bending moment, the load cell may be damaged. Contact KYOWA for applications of these types. 2. s involving shock or vibration are measured as 'static load x acceleration.' When acceler ation is unknown, be sure to prepare sufficient rated capacity. 3. With repetitive tension/compression loads, use at below 1/2 of the rated capacity in order to extend the fatigue life. 4. Special accessories are designed only for use with KYOWA load cells. 5. To avoid accidents, make sure to take precautionary measures against unforeseeable situations caused by a broken load cell. 1)Tension load cells Use special accessories assembled and incorporated into the load cell by KYOWA. When loads are suspended, select a rated capacity that will ensure an adequate safety factor, and add safety devices to prevent loads from dropping. (With static breaking loads, see the table of dimensions for special accessories.) The tension load cell is joined to the counterpart by screws. Be sure to prevent screws from loosening. If set screws are used for this purpose, counter bore the mating parts to fit set screws. Also, check regularly for any loosening of set screws. 2)Compression load cells In the event that the strain column of the load cell buckles, the height is reduced by up to several tens of mm. The load is thereafter supported by the outer case. Examine the effect of such dimensional changed on the load cell installation area and equipment. 6. Check periodically to make sure the load cell fixing screws have not become loose. If looseness is found, tighten completely. 7. Contact KYOWA concerning usages involving legal safety factors, etc. (cranes, etc.) 2-3

3 Various Shapes of Cell Strain Column Linear Beam Type Bending Force Sensing Type Hollow Cylindrical Type 2-4 Shearing Force Sensing Type (Beam Type) Fixed Installation of Cell and Special Accessories (for Accurate Measurement) Mount Base Movable Saddle Mount Base Saddle Compression Cell 1. Fix the steel plate to the load point of measuring object by welding or screwing. Mount the saddle to the steel plate. Grease the saddle to prevent it from rusting. 2. Install the saddle and mount base horizontal to the load cell so that a load is applied vertically to the load cell. 3. Each load cell is designed to detect only the force applied to the central axis. Since installation quality directly affects the measurement accuracy, install it carefully so that an inclined load, angular moment, horizontal force component and bending moment may not affect the load cell. 4. cell is capable of compensating daily temperature changes. However, if it is partially heated, the accuracy may adversely be affected transiently. If it is not avoidable to use at temperatures beyond the operating temperature range, protect the load cell with a heat insulating material to keep it in the operating temperature range. 5. If there is impact or vibration in the loading direction, it is difficult to determine the rated capacity of load cell unless the magnitude of acceleration is known. In such a case, select a load cell of which the rated capacity is sufficient enough. If the magnitude of acceleration is known, obtain the product of 'mass x acceleration' as the rated capacity. If the tare is included in the mass, determine the rated capacity by adding it to the net weight. For details, see page Ball Joint Rotary Attachment Shackle Ball Joint Rotary Attachment Hook Tension Cell 1. Using the screw at the center of the top and the bottom, install the tension load cell carefully so that any bending or angular moment may not be applied to the load cell during measurement. Such a moment not only affects the measurement accuracy but also causes an overload which may lead to breakage of the load cell. 2. For safe operation, select rated capacity sufficient enough to cover unsuspected loads. Also, prepare safety devices against accidental hazards such as dropping. 3. Operation near the rated capacity with a special accessory (TR, TH, TU, RJ or the like) attached or an overload may cause a problem on mechanical strength depending on the installation method. For solutions of such a problem, contact us. 4. When mounting the RJ-B rotating attachment, remove the coupling screw of load cell in advance. Proper tightening torque for mounting is shown at the right. 5. When screwing a ball joint into the load cell, take care not to apply any excess torque to the load cell. Especially, a small-capacity load cell may be damaged by an excess torque. Rated Capacity Tightening bolt Tightening torque (approx.) 0.5~2kN 5~20kN 50kN 100kN 200kN M6 10N m M8 30N m M10 70N m M16 270N m M20 560N m 2-4

4 BRIDGE UNIT DBU-120A SYNC OUT IN ID 2-5 Measuring System Block Diagrams Indication, Measurement, Control & Monitor Measurement of Dynamic Phenomena Cell Pressure Torque Displacement Instrumentation Amplifier WGA Output RS- 232C (Monitor Display High/Low Limit Contact Output Printer Cell Bridge Unit DBU-120A Sensor Interface D Series USB Compact Recorder EDS-400A Other s Note: 's connector and cable differ depending on models. For details, refer to description of each model and Chapter 8. In combination use of pressure transducer and instrumentation conditioner in WGA series, the measuring range is rarely exceeded due to initial unbalance of the transducer. For details, contact us. Pressure Acceleration Universal Recorder EDX-100A CF Card USB Torque Memory Recorder/ Analyzer EDX-3000A Displacement Multi Conditioner D-A Other s A-D Converter Strain Amplifier DPM Signal Conditioner CDV,CDA-700A Recorder 2-5

Pressure RS-232C Data Logger UCAM-60B Torque RS-232C Displacement Data

5 2-6 Measurement of Static Phenomena with Data Loggers Required for multi-channel measurement Cell Fast Data Logger UCAM-500B Scanner USB Pressure RS-232C Data Logger UCAM-60B Torque RS-232C Displacement Data Logger UCAM-65B Other CAN CAN-USB Converter USB Network Terminal Box. NTB Series 2-6

6 2-7 Cells Measurement Example Displacement Measurement of Plate Bearing Test Weight Control of Hopper Tank 2-7

7 2-8 Control of Press Machine 6-Component Force Measurement of an Artificial Leg or Robot with Built-In Cells 2-8

GENERAL CATALOG

LOAD CELLS GENERAL CATALOG 15 16 ZSE Electronic Mess-Systeme & Sensortechnik GmbH In den Freßäckern 28 D-74321 Bietigheim-Bissingen Telefon: 07142 6845 - Fax: 07142 6997 e-mail: info@zse.de - www.zse.de