Emerson Process Management 396PVP Section Maintenance, 6.1AUTOMATIC TEMPERATURE COMPENSATOR

MODEL 396P and 396PVP	SECTION 6.0
	MAINTENANCE

SECTION 6.0

MAINTENANCE

The Model 396P and 396PVP Sensors require mini- mum maintenance. The sensor should be kept clean and free of debris and sediment at all times. The fre- quency of cleaning by wiping or brushing with a soft cloth or brush is determined by the nature of the solu- tion being measured. The sensor should be removed from the process periodically and checked in buffer solutions.

WARNING

BEFORE REMOVING THE SENSOR, be absolutely certain that the process pres- sure 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 proce- dures. If it is determined that the sensor has failed, it should be discarded and replaced.

6.1AUTOMATIC TEMPERATURE COMPENSATOR.

The temperature compensator element is temp- erature sensitive and can be checked with an ohm- meter. Resistance increases with temperature.

The 3K element will read 3000 ohms ± 1% at 25°C (77°F) and a Pt100 will read 110 ohms. Resistance varies with temperature for a 3K and Pt100 element and can be determined according to Table 6-2 or the following formula:

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

Where RT = Resistance

T = Temperature in °C

Refer to Table 6-1 for Ro and R1 values

6.2 MODEL 396P & 396PVP pH SENSORS

4.2.1ELECTRODE CLEANING. If the electrode is coated or dirty, clean as follows:

1.Remove the sensor from process.

2.Wipe the glass bulb with a soft, clean, lint free cloth or tissue. If this does not remove the dirt or coating, go to Step 3. (Detergents clean oil and grease; acids remove scale.)

3.Wash the glass bulb in a mild detergent solution and rinse it in clean water. If this does not clean the glass bulb, go to Step 4.

CAUTION

The solution used during the following check 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 skin is made, immediately rinse with clean water.

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.

NOTE

Erroneous pH results may result immedi- ately after acid soak, due to reference junction potential build-up.

Replace the sensor if cleaning does not restore sensor operation.

TABLE 6-1

Ro and R1 VALUES FOR TEMPERATURE

COMPENSATION ELEMENTS

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

TABLE 6-2

TEMPERATURE vs RESISTANCE OF AUTO

T.C. ELEMENTS

	Resistance
Temperature °C	(Ohms) ±1%
	3K	Pt100
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

25