Emerson Rosemount 385, Reference Manual, Page: 20 / 34

14 Maintenance
Maintenance Reference Manual
February 2019 00809-0100-3385
4. Wash the glass bulb in a dilute 5% hydrochloric acid solution and rinse with clean water.
Soaking the sensor overnight in the acid solution can improve cleaning action.
Replace the sensor if it cannot be cleaned.
4.2.2 Automatic Temperature Compensator
The temperature compensator element is temperature sensitive and can be checked with an
ohmmeter. Resistance increases with temperature.
The 3K element will read 3000 ohms ±1% at 25°C (77°F) and a Pt-100 will read 110 ohms.
Resistance varies with temperature for a 3K and Pt-100 element and can be determined
according to Table 6-2 or the following formula:
RT=R0 [l+R1 (T-20)]
Where RT = Resistance
T = Temperature in °C
Refer to Table 4-1 for R0 and R1 values
The solution used in the following step is an acid and should be handled with care. Follow the directions of the
acid manufacturer. Wear the proper protective equipment. Do not let the solution come in contact with skin
or clothing. If contact with the skin is made, immediately rinse with clean water.
CAUTION
Table 4-2: R
0
and R
1
Values for Temperature Compensation Elements
Temperature Element R
0
R
1
3K 2934 0.0045
PT-100 107.7 0.00385
Table 4-1: Temperature vs Resistance of Automatic Temperature Compensator Elements
Temperature °C Resistance (Ohms) ±1
3K PT-100
0 2670 100.0
10 2802 103.8
20 2934 107.7
25 3000 109.6
30 3066 111.5
40 3198 115.4
50 3330 119.2
60 3462 123.1
70 3594 126.9
80 3726 130.8
90 3858 134.6
100 3990 138.5