Serious errors in calibration and display can result if the wrong sensor type is selected on the controller versus what is actually wired to it. Only a physical check of sensor wire and sensor prompts can detect this condition. A systems validation test checking at several temperature points with an external calibrator or measurement device is highly recommended. See chart below.

This is especially important if using a hi-limit sensor, as the limit sensor may be set incorrectly and will not shut down the system safely in the case of an overtemp condition.

Below are examples of improper readings shown when the controller is set up for default Type J sensor:

100°F Sensor Temperature 500°F Sensor Temperature
Sensor Wired for: Displayed Temp. Displayed Temp.
B 71.8°F 84°F
C 85°F 207°F
D 85°F 207°F
E 105°F 617°F
K 96°F 394°F
N 90°F 321°F
R 81°F 143°F
S 81°F 141°F
T 96°F 459°F
100 ohm RTD Ambient Ambient
1,000 ohm RTD Ambient Ambient
Thermistor Ambient Ambient
0-20mA Eri1 Eri1
0-5 mV Ambient 407

This information was excerpted from a Watlow White Paper titled “Controls Integration White Paper” and may be found on Watlow’s website.

IES Technical Sales provides technical sales and distribution support to users and OEMs, with focus in the northeast U.S., and is an authorized Watlow distributor.