The MBE-1 Humidistat is essentially a single pole, double throw microswitch, operated by an actuating element that is extremely sensitive to changes in the relative humidity. When the relative humidity either rises or drops above the control setting, the switch is activated and thrown in the proper direction.
The Type MBWE-1 Humidistat operates in the same manner as the Type MBE-1, but is equipped with a weekend control lever. This added feature allows a decrease in the humidity for shut-down periods without changing the normal control setting
The setting may be adjusted to any point from on to 30 percent below the normal setting.
The design of these Humidistats allow the original settings to be made with extreme accuracy. When changes are required, the control is adjusted by rotating the dial cap at the top of the humidistat. This cap has graduations on the rim and a pointer indicating the direction in which the cap should be turned to raise or lower the relative humidity. One gradation represents a change of approximately 1 percent.
The MBE-1 and MBWE-1 Humidistats were designed with the extreme conditions required in industrial and commercial applications. These controls are not limited to any on type of application. These humidistats have been successfully used for over 60 years in extreme conditions and proven completely dependable. The use of an electrical circuit makes its application a must when a positive control is required.
1. A sling psychrometer should always be used to determine the relative humidity in the control area. Direct reading hygrometers or stationary wet and dry bulb thermometers are not sufficiently accurate for this purpose.
2. At the top of the humidistat is a Dial Cap No. B-3 with graduations around the rim. The Pointer No. B-16 indicates the direction in which the cap should be turned to raise or lower the humidity. A movement of one graduation represents a change of 1 percent. The numbers around the rim of the cap are for reference only.
3. With a sling psychrometer determine the humidity in the area. If your reading is below the required level turn the dial cap B-3 in the direction to raise and allow the humidity to build up till the control cycles the humidifier off. Note when you turn the dial cap, you will feel a click. Each click corresponds to the gradation on the dial cap and indicates a change of 1 percent in humidity.
4. With the psychrometer determine the new humidity level in the area when the control point is reached. If the level is still incorrect turn the dial cap in the proper direction to either raise or lower the level. Continue the procedure until the proper humidity level is reached. Allow the control to operate through several cycles then recheck the humidity level with the psychrometer. Remember that when a considerable change is made in the control setting several cycles of operation are required before the actuating element attains a permanent setting.
5. When the adjustment has been correctly made loosen the top cap nut No. B-8 and rotate the cap until the 0 division is opposite the index. Then tighten the top cap nut. The 0 division now represents the desired humidity level. Rotation of the cap in ether direction will raise or lower the level.
6. Later adjustments. After the system has been in operation for some time it may be necessary or desirable to change the control setting. This should be done in the same manner as the start up procedure.
The initial adjustment with the Type MBWE-1 should be made exactly as above withe following exceptions. The Week-end Lever No. B-58 should be positioned against the Pointer at the front. After the initial adjustment, the Weekend Stop No. B-57 should be set to give the desired decrease in relative humidity for shut-down periods. For example, if the humidity is to be reduced 15 percent the total change in setting is 30 percent when the stop is as far back as it will go. The stop should be set about half way back and the lever moved back against it. A check of the humidity may indicate that the stop should be moved a little, either forward or back. When the stop is correctly located, it should be clamped in place. During normal operation, the lever should be against the pointer at the front and against the stop for periods of reduced humidity.