Emerson Combination pH/ORP Sensor Section Maintenance, General, Automatic Temperature Compensator

MODEL 399VP pH/ORP SENSOR	SECTION 5.0
	MAINTENANCE

SECTION 5.0.

MAINTENANCE

5.1GENERAL

5.2AUTOMATIC TEMPERATURE COMPENSATOR

5.3pH ELECTRODE CLEANING

5.4ORP PLATINUM ELECTRODE CHECK

5.1GENERAL

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.

5.2AUTOMATIC TEMPERATURE COMPENSATOR

The temperature compensator element is temperature 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:

RT = Ro [l+R1 (T-20)]

Where RT = Resistance

T = Temperature in °C

Refer to Table 5-1 for Ro and R1 values

TABLE 5-1. Ro and R1 VALUES FOR

TEMPERATURE COMPENSATION ELEMENTS

Temperature	Ro	R1
Compensation Element
3K	2934	.0045
Pt100	107.7	.00385

TABLE 5-2. TEMPERATURE vs RESISTANCE

OF AUTO T.C. ELEMENTS

	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

21