Operating instruction manual
| TX Thermal Disperson Level Switches 17
8.0 TEMPERATURE SWITCH OPTION
In the temperature switch configuration, the heater can be disabled and the active RTD is not used. The reference RTD
is used to measure the temperature of the process medium. The resistance of the reference RTD is directly propor-
tional to temperature. The unit is shipped with the default settings unless otherwise stated on the order. A temperature
set point can be verified or changed by placing a resistance decade box across pins 1 & 2 of connector P2. Pin 1 is
located closest to the edge of the board. Once the desired set point temperature has been decided, the resistance of
the decade box can be used to set the point where the relay energizes (LED on):
TABLE 1
: OHMS / Deg. F for silicone temperature sensor
-
Standard
Resistance calculation = [(0.0053(temp in degrees F) ²) + 3.4187(temp in degrees F) + 704.99] ohms.
TEMP F
0
+5
+10
+15
+20
+25
+30
+35
+40
+45
-50
547
562
577
592
607
623
639
655
671
688
0
705
722
740
757
775
794
812
831
850
870
50
889
909
929
950
970
991
1012
1034
1056
1078
100
1100
1122
1145
1168
1192
1215
1239
1263
1287
1312
150
1337
1362
1388
1413
1439
1466
1492
1519
1546
1573
200
1601
1629
1657
1685
1714
1743
1772
1801
1831
1861
250
1891
1921
1952
1983
2014
2046
2078
2110
2142
2175
300
2208
2241
2274
2308
2342
2376
2410
2445
2480
2515
350
2551
2587
2623
2659
2695
2732
2769
2807
2844
2882
TABLE 2
: OHMS / Deg. F - HIGH TEMP OPTION (/H1 or /H2): (Platinum RTD)
Resistance calculation = [(-0.0002(temp in degrees F) ²) + 2.1288(temp in degrees F) + 932.05] ohms.
TEMP F
0
+10
+20
+30
+40
+50
+60
+70
+80
+90
-300
275.4
297.9
320.3
342.7
365
387.4
409.6
431.8
450
476.2
-200
498.3
520.4
542.4
564.4
586.3
608.2
630.1
651.9
673.7
695.5
-100
717.2
738.8
760.5
782.1
803.6
825.1
846.6
868.0
889.4
910.7
0
932.1
953.3
974.5
995.7
1016.9
1038.0
1059.1
1080.1
1101.1
1122.0
100
1142.9
1163.8
1184.6
1205.4
1226.2
1246.9
1267.5
1288.2
1308.8
1329.3
200
1349.8
1370.3
1390.7
1411.1
1431.4
1451.8
1472.0
1492.2
1512.4
1532.6
300
1552.7
1572.8
1592.8
1612.8
1632.7
1652.6
1672.5
1692.3
1712.1
1731.9
400
1751.6
1771.2
1790.9
1810.5
1830.0
1849.5
1869.0
1888.4
1907.8
1927.1
500
1946.5
1965.7
1984.9
2004.1
2023.3
2042.4
2061.5
2080.5
2099.5
2118.4
600
2137.3
2156.2
2175.0
2193.8
2212.6
2231.3
2249.9
2268.6
2287.2
2305.7
700
2324.2
2342.7
2361.1
2379.5
2397.8
2416.2
2434.4
2452.6
2470.8
2489.0
800
2507.1
2525.2
2543.2
2561.2
2579.1
2597.0
2614.9
2632.7
2650.5
2668.3
900
2686.0
2703.6
2721.3
2738.9
2756.4
2773.9
2791.4
2808.8
2826.2
2843.5
Example 1: At (-20 F) (Standard RTD) the resistance is
639
ohms (see table1)
Example 2: Using platinum RTD, the resistance at –20 °F is calculated as follows:
Set Point Resistance = (0.0002)(-20) ² + 2.1288(-20) + 932.05 = 889.6 ohms (Table 2 = 889.4 ohms)
With the resistance decade box connection across pins 1 & 2, adjust R18 until the LED just turns off. Decreasing the
resistance of the decade box now will cause a drop in temperature and resistance, and the relay to energize and the
LED to turn on.
State A is the default configuration
for the relay from the factory. Other jumpers must be move to set the switch for
temperature operation. The relay is de-energized (LED off) until the temperature drop below the set point. If it is de
-
sired that the relay energize when the temperature rises above the set point then configure JP3 for State B.
