Armstrong World Industries EHU-701, EHU-703 manual Operational Guidelines, Tank Contactor Operation

A high-water float switch prevents water carry-over into the duct due to an excessive water level in the tank. When the high water limit is reached the HIGH WATER light comes on and the fill valve is blocked until some water is boiled away and the water level drops. This is common during startup. If the high water light comes on and the water level is in the lower half of the steam generator, contact the factory for assistance. This is due to high static pressure. Installation of fill cup extension kit could be required.

If an overcurrent situation is detected, the overcurrent protection circuit will drain water from the tank to reduce current flow. If the overcurrent persists, the contactor will be de-energized to stop all current flow.

The Series EHU-700 patented automatic capacity adjustment feature eliminates manual adjustment and improves humidity control. This feature automatically adjusts maximum output up or down depending on the humidity demand history. When the unit is first turned on the maximum output is 40%. If the demand stays high, the unit automatically steps up the maximum output and will reach 100% maximum output after one hour. For test purposes, or for special operating situations, this fea- ture can be easily over-ridden by changing the position of jumper BJ1 on the printed circuit board from pins 1 and 2 to pins 2 and 3.

An automatic drain cycle blows down mineral-laden water to increase steam generator life and reduce maintenance requirements. The frequency and duration of the drain cycle will vary with supply water conductivity, steam output, and humidistat demand history. When it is initiated automatically, the drain valve cycle occurs at the beginning of a fill cycle. The incoming cold water tempers the drain water to less than 160ºF after 72 hours of no demand, the unit will initiate an "End-of-Season" drain to remove stagnant water.

OPERATIONAL GUIDELINES

This section describes the conditions and indications you should expect to find in a normally operating humidifier.

Tank Contactor Operation:

The microcontroller will de-energize the contactor, turning off the current to the electrodes if ANY of the following occur:

1.The control humidistat demand signal is less tan 25%.

2.The fan interlock circuit is open.

3.The high limit humidistat circuit is open.

4.The tank current is greater than the over-current limit.

Conversely, the microcontroller will energize the contactor, turning on the current to the electrodes, only if ALL of the following occur:

1.The control humidistat demand signal is greater than 35%.

2.The fan interlock circuit is closed.

3.The high limit humidistat circuit is closed.

There is a time delay of fifteen seconds in the contactor operating circuitry to prevent it from cycling too rapidly after it has been turned off.

Monitoring Stat Demand:

Indicates the demand for humidity in relationship to the control range of the humidistat. 0% indicates that the humidity requirement has been exceeded. 100% indicates that the humidistat is calling for full humidifier output. In general, a reading of around 50% indicates that the set point has been met.

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