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MODEL 399VP pH/ORP SENSOR SECTION 5.0
MAINTENANCE
SECTION 5.0.
MAINTENANCE
5.1 GENERAL
The Model 399VP sensor is a disposable type sensor and therefore requires minimum maintenance. The sensor
should be kept clean and free of debris and sediment at all times. The frequency of cleaning, by wiping or brush-
ing with a soft cloth or brush, is determined by the nature of the solution being measured. The sensor should be
removed from the process periodically and checked in buffer solutions.
WARNING
BEFORE REMOVING THE SENSOR, be absolutely cer-
tain that the process pressure is reduced to 0 psig and
the process temperature is lowered to a safe level!
If the sensor will not calibrate, refer to your analyzer/ transmitter instruction manual for proper test procedures. If
it is then determined that the sensor has failed, it should be discarded and replaced.
5.2 AUTOMATIC TEMPERATURE COMPENSATOR
The temperature compensator element is temp erature sensitive and can be checked with an ohmmeter.
Resistance increases with temperature.
Resistance varies with temperature for a 3K and Pt100 element and can be determined according to Table 5-2 or
with the following formula:
R
T
= R
o
[l+R
1
(T-20)]
Where R
T
= Resistance
T = Temperature in °C
Refer to Table 5-1 for R
o
and
R
1
values
5.1 GENERAL
5.2 AUTOMATIC TEMPERATURE COMPENSATOR
5.3 pH ELECTRODE CLEANING
5.4 ORP PLATINUM ELECTRODE CHECK
Resistance
Temperature °C (Ohms) ±1%
3K Pt100
0 2670 100.0
10 2802 103.9
20 2934 107.8
25 3000 109.7
30 3066 111.7
40 3198 115.5
50 3330 119.4
60 3462 123.2
70 3594 127.1
80 3726 130.9
90 3858 134.7
100 3990 138.5
Temperature
Compensation Element
R
o
R
1
3K 2934 .0045
Pt100 107.7 .00385
TABLE 5-2. TEMPERATURE vs RESISTANCE
OF AUTO T.C. ELEMENTS
TABLE 5-1. R
o
and R
1
VALUES FOR
TEMPERATURE COMPENSATION ELEMENTS