MODEL 396/396VP/397/398/398VP | SECTION 4.0 |
| MAINTENANCE |
SECTION 4.0
MAINTENANCE
4.0MAINTENANCE. The Model 396, 396VP, 397, 398, and 398VP Sensors are disposable type sensors and therefore require minimum maintenance. Every sensor should be kept clean and free of debris and sediment at all times. The frequency of cleaning by wiping or brushing with a soft cloth or brush is deter- mined by the nature of the solution being measured. The sensor should be removed from the process peri- odically and checked in buffer solutions.
SAFETY WARNING
SENSOR IS IN PRESSURIZED SYSTEM!
May cause spray and bodily injury. Before removing sensor, be absolutely certain 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 proce- dures. If it is determined that the sensor has failed, it should be discarded and replaced.
4.1ELECTRODE CLEANING. If the electrode is coat- ed or dirty, clean as follows:
1. Remove the sensor from process.
SAFETY WARNING
SENSOR IS IN PRESSURIZED SYSTEM may cause spray and bodily injury.
Before removing sensor, be absolutely cer- tain that the process pressure is reduced to 0 psig and the process temperature is low- ered to a safe level.
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 strong 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, immedi- ately 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 occur immedi- ately after acid soak, due to reference junction potential
Replace the sensor if cleaning does not restore sensor operation.
4.2AUTOMATIC 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
RT=Ro [l+R1
Where RT = Resistance
T = Temperature in °C
Refer to Table
TABLE
Temperature Compensation Elements
| Temperature |
| Ro |
| R1 |
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| Compensation Element |
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| 3K |
| 2934 |
| .0045 |
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| 107.7 |
| .00385 |
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| TABLE |
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| of Auto T.C. Elements |
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| Temperature °C |
| Resistance (Ohms) ±1% |
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| 3K |
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| 0 |
| 2670 | 100.0 |
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| 10 |
| 2802 | 103.8 |
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| 20 |
| 2934 | 107.7 |
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| 25 |
| 3000 | 109.6 |
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| 30 |
| 3066 | 111.5 |
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| 40 |
| 3198 | 115.4 |
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| 50 |
| 3330 | 119.2 |
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| 60 |
| 3462 | 123.1 |
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| 70 |
| 3594 | 126.9 |
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| 80 |
| 3726 | 130.8 |
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| 90 |
| 3858 | 134.6 |
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| 100 |
| 3990 | 138.5 |
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