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Maintenance
February 2019
4.2
Automatic temperature compensator
The temperature compensator element is a temperature sensitive resistor and can be
checked with an ohmeter. Resistance increases with temperature.
The 3K element reads 3000 ohms ±1% at 77 °F (25 °C), and a Pt100 reads 110 ohms.
Resistance varies with temperature for a 3K and Pt-100 element and can be determined
according to
R
= R
T
Where R
Refer to
Table 4-1: R
Temperature compensation
element
3K
PT-100
Table 4-2: Temperature vs. Resistance of Auto T.C. Elements
Temperature °C
0
10
20
25
30
40
50
60
70
80
90
100
32
Refer to
Startup and
calibration. If the sensor appears to respond sluggishly to pH
change, soaking it overnight in a weak acid solution (5% hydrochloric acid) may
improve its response. Be sure to follow the Warning above and to rinse the sensor's
tip thoroughly with tap water. If the sensor will not calibrate, it must be replaced.
Table 4-2
or the following formula:
[1 + R
(T-20)]
O
1
= Resistance and T = Temperature in °C
T
Table 4-1
for R
and R
O
and R
Values for Temperature Compensation Elements
O
1
values.
1
R
O
2934
107.7
Resistance (Ohms) ±1%
3K
26270
2802
2934
3000
3066
3198
3330
3462
3594
3726
3858
3990
Reference Manual
00809-0100-3389
R
1
0.0045
0.00385
PT-100
100.0
103.8
107.7
109.6
111.5
115.4
119.2
123.1
126.9
130.8
134.6
138.5
Rosemount 389/389VP
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