Watlow Series 1500 User Manual download pdf (Page 27)

Installation-Wiring

Installation - Wiring, Chapter 3

WATLOW Series 1500 User's Manual 27

Use distilled water to avoid mineral deposits on the wick that can change the %RH

reading. The wicking distance should be as short as practical. The cotton wick must

be free of any sizing and starch. The "float valve-trough" systems should also re-

move the water when the ambient temperature goes below freezing or above boiling.

To obtain valid %RH readings, air flow past the %RH sensor must be sufficient to

evaporate the maximum amount of water from the wick without drying it out. Evapora-

tion cools the sensor; the amount of cooling relates directly to the relative humidity

present.

Thermally insulate the wet bulb sensor from the sensor mounting. This prevents

mounting surface heat from flowing into the sensor sheath and changing the wet bulb

temperature. (The result of such heat flow will be a humidity reading higher than

actual.)

Thermocouple Installation Guidelines

Locate the thermocouples in your process or system where they read average tem-

peratures. Air flow past these sensors should be moderate. The sensors must be

thermally insulated from the sensor mounting. Both thermocouples must be un-

grounded to obtain correct readings.

Wiring Practices for Preventing Noise

Most noise problems stem from wiring practices, the major means of coupling noise

from its sources to the control circuit.

An outstanding information resource for wiring guidelines is the IEEE Standard No.

518-1982 and is available from IEEE, Inc. 345 East 47th Street, New York, NY

10017.

Noise Sources

• Switches and relay contacts operating inductive loads such as motors, coils,

solenoids, and relays, etc.

• Thyristors or other semiconductor devices which are not zero crossover-fired

(randomly-fired or phase angle-fired devices).

• All welding machinery.

• Heavy current carrying conductors.

• Fluorescent and neon lights.

How to Decrease Noise Sensitivity

1. Our extensive noise testing has shown that the Series 1500 has a good level

of noise immunity. In extremely noisy environments, however, the testing has

shown that the most effective RFI techniques are:

a. An RFI filter (such as the Corcom 1ER1) in the power line mounted exter-

nal to the Series 1500 case. The RFI filter should be an RFI sealed type.

b. Shielded power cord with the shield terminated to the Series 1500 case

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Watlow Series 1500 User Manual Page 27