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4. Sensor Wiring— 6. Verifying Sensor ElectricalContinuity (Resistance)— The distancebetween sensor and instrument can be many feet. Often multiple piecesof wire are joined to complete thecircuit. Examine terminal blocks, connectors, connection heads and any other connection points for loosewires, corrosion or electrical isolation. Examine circuit wireinsulation for any damage. Replace any insulation that shows cracks,wear spots or heat deterioration withnew wiring. Verify that circuit polarityand wire orientation have beenmaintained throughout the system. Sensorsrequire a continuous electrical circuitbe formed through the resistance element or thermocouple junction.Sensor resistance can be checkedwith a standard multimeter.Resistance value of a RTD will benominal resistance at temperature of sensor plus the resistance of leadwhen checking between the leads ofdiffering colors. Between leads of the same color resistance value isequal to lead resistance. Thermocouples should haveresistance measurements taken outof application. Measurement 5. Compatible Sensor andConnection Wire— Thermocouplesrequire the connection wire conductors be of the samecalibration type as the sensor. If the calibration does not match or copperconductors are used, serious errorscan occur. The calibration type ofthermocouple wire products can usually be identified by the color of insulation. The chart on the inside back cover of this catalog shows common color codes used for thermocouple wire products. For RTDs the sensor to instrument connections are made using wire with copper conductors. Wire should be of same gauge size, copper material and length for each sensor lead.

W A T L O W

Sensor catalog - 7347 GeneralInformation

Application Hints

1. Sensor and Control Agreement—
General Information

The sensor appears to bereading incorrectly. What might be wrong?

2. Check Instrument— Verify the instrumentsettings are correct for the type of sensor being utilized. Many instruments require the user to indicate or instruct which type ofsensor will be used. Agreementbetween sensor and instrument allows correct temperatureinterpretation of the resistance or voltage. A quick testcan indicate that an instrument is functional.• Thermocouples
Application Hints Disconnect and place a jumper wire across the input connections.Instrument should indicate roomtemperature.• RTDs Ω resistor wouldindicate 0°C for a 100 Disconnect and place a known resistance value across input terminals. Instrument should indicate the temperature corre-sponding to resistor used. As anexample a 100 Ω RTD. 3. Check Instrument Connection— Verify the sensor has been attached to the correct instrument terminals. For thermocouples check that the polarity is correct. The negative conductor of thermocouples colored coded to ASTM standards is red. Other international standards use different color codes to identify thermocouple calibration and conductor polarity. The inside back cover shows many of these international color code standards. Most industrial controllers will accept a two- or three-wire RTD inputs. A two-wire RTD may or may not have the wires color coded differently and can be connected to either input terminal. A three-wire RTD generally will have two leads of one color and the third lead of a different color. The resistive element is wired in series with the leads of different colors. The instrument wiring diagram will indicate location of resistive element. 27