23
MODEL 396P and 396PVP
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.
6.1 AUTOMATIC 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
4.2.1 ELECTRODE 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.
SECTION 6.0
MAINTENANCE
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
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
Temperature
Compensation Element
Ro
R1
3K
2934
.0045
Pt100
107.7
.00385
TABLE 6-2
TEMPERATURE vs RESISTANCE OF AUTO
T.C. ELEMENTS
