ELEMENT 
ADJUSTMENT 
NUT 
ELEMENT 
MOUNTING 
PIN 
HAIR 
ELEMENT 
MERCURY 
SWITCH 
ELEMENT 
MOUNTING 
PIN 
INDICATOR 
MARK 
HUMIDITY 
aS = SCALE 
SE PLATE 
HUMIDITY 
SETTING 
KNOB 
Fig. 3—Type H61 Controller. Type H41A & B are similar 
except that they have a two-wire mercury switch. 
Care and Replacement of Hair Element—The accumu- 
lation of dust and grease on the hair element, while not harm- 
ful, may decrease the sensitivity of the controller. The element 
should be cleaned periodically with a camels hair brush and 
clean ether, followed by a complete wetting with distilled 
water. 
If the hair element should become damaged and require 
replacement, it may readily be removed by sliding out the 
element mounting pin (2) at each end of the element. When the 
new element is installed, the controller should be calibrated as 
outlined below. 
Calibration—Determine the relative humidity at a point 
close to the controller by means of a high grade sling psychro- 
meter and psychrometric chart. Do not rely on the reading 
of inexpensive relative humidity indicators to calibrate 
the controller. 
Carefully follow the instructions furnished with the psychro- 
meter, using a clean wick tightly fitted to the wet bulb, and 
distilled water at room temperature. Take at least three read- 
ings, wetting the wick before each reading. 
After determining the relative humidity of the room, turn 
the setting knob (7) to this point on the scale. Then turn the 
element adjustment nut (1) until— 
(a) H41A & B: the mercury switch “just breaks’’ contact. 
(b) H61A: the mercury switch “just breaks’ the Red and 
Blue and ‘‘makes’’ the Red and White contacts. 
M.H.R. PRINTED IN U.S.A. 
SERVICE SUGGESTIONS 
—— SETTING AND ADJUSTING —— 
SETTING —To set the Humidity Controller it is only necessary 
to turn the knurled knob (7-Fig.3) until the indicator mark (5) is 
opposite the desired percent of relative humidity on the scale (6). 
High Limit Stop—Humidity Controllers are equipped 
with an adjustable high limit “'stop’’ to prevent setting the 
indicator above the maximum desired point. 
The stop is factory set at maximum, but may be changed as 
follows: Loosen the clamp nut (9-Fig. 4). Turn the setting knob 
(7) until the pointer is opposite the maximum desired reading 
on the scale. Then rotate the cam (11) until the pin (10) rests 
against the rotor piece (8). Tighten the clamp nut (9) to hold 
the stop in place. 
HUMIDITY 
SETTING 
Fig. 4— Adjustable stop for maximum setting. 
The controller should then be in proper calibration. How- 
ever, the heat and moisture from your body may have affected 
the calibration by several percent, and the adjustment should 
therefore be checked. Move away from the controller for 
at least 15 minutes. Then turn the setting knob (7) until the 
scale registers the actual relative humidity of the room (as 
previously measured by the sling psychrometer) and note 
whether the position of the mercury switch or potentiometer 
slider corresponds with that outlined under (a) or (b) above. 
If not, turn adjusting nut (1) slightly and recheck the adjustment. 
Fig. 5—Terminal Arrangements in Older Models. 
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