tekmar 521 Programmable Thermostat Installation - Manual (Page 8)

© 2014 521_D - 01/14
8 of 28 A Watts Water Technologies Company
Slab Sensor 079 Testing
A good quality test meter capable of measuring up to 5,000 kΩ (1 kΩ = 1000Ω) is
required to measure the sensor resistance. In addition to this, the actual temperature
must be measured with either a good quality digital thermometer, or if a thermometer
is not available, a second sensor can be placed alongside the one to be tested and
the readings compared.
First measure the room temperature using the thermometer. Disconnect the S1 or S2
and Com wires from the thermostat. Using an electrical meter, measure the resistance
of the S1 or S2 and Com wires at the thermostat location. Using the temperature
versus resistance table, estimate the temperature measured by the sensor. The sensor
measurement and thermometer readings should be close. If the test meter reads a very
high resistance, there may be a broken wire, a poor wiring connection or a defective
sensor. If the resistance is very low, the wiring may be shorted, there may be moisture
in the sensor or the sensor may be defective. To test for a defective sensor, measure
the resistance directly at the sensor location. Once the test has been completed,
reconnect the S1 or S2 and Com wires to the thermostat.
Do not apply voltage to the temperature sensor terminals at any time as damage to
the sensor may result.
Temperature vs. Resistance Table
Temperature Resistance
°F °C
-50 -46 490,813
-45 -43 405,710
-40 -40 336,606
-35 -37 280,279
-30 -34 234,196
-25 -32 196,358
-20 -29 165,180
-15 -26 139,402
-10 -23 118,018
-5 -21 100,221
0 -18 85,362
5 -15 72,918
10 -12 62,465
15 -9 53,658
20 -7 46,218
Temperature Resistance
°F °C
25 -4 39,913
30 -1 34,558
35 2 29,996
40 4 26,099
45 7 22,763
50 10 19,900
55 13 17,436
60 16 15,311
65 18 13,474
70 21 11,883
75 24 10,501
80 27 9,299
85 29 8,250
90 32 7,334
95 35 6,532