Humidity Alarm

Introduction

Ohmic model HCLS 20/99-AL Air Line Humidity Alarm is designed to monitor the relative humidity in a pressurized air system and provide alarm output conditions when the air line humidity exceeds a preset humidity level. The unit is constructed in a weather-tight NEMA 12 enclosure. The humidity level in the air line is sensed by an Ohmic weatherproofed humidity sensor model UPS-600RS, which is mounted using a model HPM-350 high pressure mount. This high pressure mount is installed into the pressurized environment using 1″ NPT fittings. A 12′ sensor cable model CH-12 is used to connect the humidity sensor to the alarm system.

Model HCLS 20/99-AL provides a direct indication of humidity in the pressurized environment on a color-zoned analog meter on the front panel. The color zones apply to a typical 85% setpoint application, but the setpoint may be adjusted for any humidity value between 20% and 99%. The setpoint is adjusted from the front panel by simply depressing the push-to-read button and turning the alarm setpoint adjustment until the desired humidity alarm level is indicated on the meter. The setpoint adjustment has a locking nut which should be tightened after the desired setpoint is obtained to minimize tampering. The unit is factory set to activate the alarm conditions when the humidity rises above the alarm setpoint. An alarm condition will be indicated by a flashing LED on the front panel, a pulsed (or continuous) audible alarm, and contact closures on humidity rise above or below the setpoint value. These contact closures can be used for external humidity control of the pressurized air.

The unit is powered from a 12 VDC power source which can be supplied either through the 25-pin D-type output connector, or by using the included plug-in 120 VAC to 12 VDC power supply which supplies power through a 1/8″ jack on the bottom of the enclosure. The accuracy of the model HCLS 20/99-AL is ±1% relative humidity at an operating temperature of 80°F. A negative temperature coefficient of -3% relative humidity per +20°F change from 80°F can be used to correct measurements at other operating temperatures.

1. Relative Humidity Meter Display
   This meter displays the relative humidity value in % measured in the pressurized air line at a temperature of 80°F. The scale is color zoned with green (safe), yellow (caution), and red (alarm) for a typical 85% alarm application.
2. Alarm Setpoint Pushbutton
   Depressing this setpoint pushbutton causes the meter to display the alarm setpoint. Make sure the button is firmly pushed until a distinct click is noticed.
3. Alarm Setpoint Adjustment
   This lockable adjustment will change the alarm setpoint to any humidity value within the 20% to 99% operating range. The alarm setpoint pushbutton should always be pushed while making this adjustment.
4. 7-Pin Sensor Input Connector
   This connector accepts the 7-pin male connector from the sensor cable.
5. Output Connector
   This is a 25-pin D-type connector which provides the following connections:

   Pin 1	Analog Ground
   Pin 2	Analog Voltage Output (0 to 1 VDC)
   Pin 3	Common Contact Output
   Pin 4	Close-On-Fall Contact
   Pin 5	Close-On-Rise Contact
   Pin 14	Power Supply Ground
   Pin 25	+12 VDC Input

6. Audible Alarm
   This piezoelectiric alarm emits a penetrating 2900 Hz pulsed signal at about 70 dB during a high humidity alarm condition. The alarm signal can be changed from pulsed to continuous operation by moving the (pulse) terminal wire to the (-) terminal.
7. High Humidity Warning LED
   The LED (Light Emitting Diode) will flash at a rate of 3 Hz whenever the humidity exceeds the alarm setpoint.
8. 12 VDC Power Input Jack
   Plug the 12 VDC external power supply into this jack to power the unit. Optionally, power may be applied through the output connector, making certain of correct polarity (some circuitry is polarity-protected, but reversed polarity may cause some permanent damage).
9. Power LED
   This LED is illuminated when power is applied to the unit.

Operating Instructions

1. Pipe a 1″ tee fitting, short nipple and a 1″ pipe coupling into the air line as shown in the attached diagram. Be sure that the arrangement is inverted so that water in the air line does not accumulate on the sensor element. Insert the UPS-600RS into the HPM-350 and insert this assembly into the coupling.
2. Connect the female end of the CH-12 cable onto the two connector pins in the HPM-350. Connect the male end of this cable into the sensor input connector on the bottom panel of the alarm unit.
3. Apply power to the HCLS 20/99-AL using the external 12 VDC power supply or through the output connector pin 14 (-) and pin 25 (+). If the humidity is within the relative humidity measurement range, the meter will read upscale; low relative humidity will cause downscale readings. To verify system operation, remove the sensor mounting from the air line and blow lightly on the sensor. This will cause a humidity increase and a corresponding upscale deflection. The alarm will activate if the humidity exceeds the alarm setpoint.
4. Check the alarm setpoint by depressing the push-to-read button on the front panel. The unit is factory preset at 85% relative humidity. Trip point may be readjusted by turning the setpoint adjustment on the front panel until the meter indicates the desired relative humidity alarm value. Be sure to firmly depress the pushbutton until a distinct click is noticed when checking or adjusting this setpoint.
5. Connect the external control system to the alarm contact pins (in the output connector on the bottom panel).
6. At this point, the unit should be operating adequately.

Troubleshooting

When the humidity alarm sounds, the humidity of the compressed air going to the air bearing spindles has risen above the setpoint on the humidity alarm.

Take These Steps Immediately to Reduce Humidity in the Air System

1. Lock the spindle with the rotor lock. Locking the spindle prevents damage by inadvertent rotation.
2. Reduce the inlet pressure to approximately 60 psi. This will immediately lower the humidity. The bearing should not be operated at this pressure.
3. Replenish the dryer pellets.
   1. Attach a regulated air supply to the alternate air inlet (40 psi is recommended). The alternate air supply should be dry, oil-free air or dry nitrogen. The alternate air supply is used for a short period of time, while replacing the dryer pellets. A shuttle valve prevents back-flow of the alternate air supply through the dryer. Professional Instruments Company recommends the Koby “Junior King” air purifier as a final filter for this air supply.
      
      Koby Incorporated
      297 Lincoln Street
      Marlboro, MA 01752 USA
      (508)481-1131 Phone
      (508)481-1136 Fax
      
   2. Reduce the main air supply to zero psi.
   3. Open the drain on the bottom of the dryer to relieve the pressure in the tank.
   4. Open the top of the dryer tank and pour in fresh deliquescent pellets. Fill to the top of the sight glass.
   5. Repressurize the system to 130 psi minimum.
   6. Note the humidity level on the humidity alarm. If a safe humidity level has not been reestablished, contact Professional Instruments.

Cautionary Notes

Any humidity level under 85% relative humidity is acceptable. Zero percent humidity in the air is impossible to achieve. The lower the relative humidity, the better. The humidity level should be checked every day. Because mechanical (i.e. refrigerating or regenerative) air drying systems tend to fail suddenly, it is best to be aware of the normal humidity level so that any sudden changes will be noticed.

The deliquescent pellets in the dryer are consumed by the drying process. The moisture in the air combines with the salt in the deliquescent pellets. The water/salt solution drips to the bottom of the dryer and is drained by opening the yellow-handled valve on the bottom of the air dryer tank. Check the level of the pellets at least once each month, replenishing them as necessary. The residue in the bottom of the air dryer will need to be cleaned out after two to three years of use. A vacuum cleaner and a blunt probe work well to remove this.

Technical Specifications

Replacement Parts

The above parts are available from:

Ohmic Instruments Company
508 August Street
Easton, MD 21601
Phone (410)820-5111
www.ohmicinstruments.com

Attachment
HumidityAlarmManual.pdf