Herrtronic
®
MD Series
Installation, Operation, & Maintenance Manual
5
www.herrmidifier-hvac.com
Types of Control
The Herrtronic MD System is available with (3) types of con-
trol ---(1) On/Off, (2) Proportional, (3) Proportional + Integral:
1. On/Off – Humidity is sensed by a humidistat that pro-
vides an On/Off input to the humidier. Humidity varies
above and below the setpoint based on the tolerance
and accuracy of the humidistat.
2. Proportional – A proportional controller produces a sig-
nal (ohms, volts DC, or milliamps DC) corresponding to
the difference between the control humidity and the hu-
midity setpoint. The humidier’s output increases as this
difference (and signal) increases. Humidity variations
will be smaller than with “On/Off” control and the control
humidity will be maintained within the bandwidth, toler-
ance, and accuracy of the controller.
3. Proportional + Integral – Over a repeating time period
the “P+I” control simply evaluates the difference be-
tween the average control humidity and the control hu-
midity setpoint and adjusts the bandwidth to minimize
the “offset.” Optimal control is attained in most cases
with this alternative.
NOTE
If your application is unique or water is excessively
“clean” or “dirty,” consult Herrmidier for assis-
tance in matching your humidier, water treatment,
and its control scheme to your application!
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0 5 10 15 20 25 30 35 40 45 50 55
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55
60
Types of Control
Offset Correction
On/Off Control
Proportional Control
Proportional + Integral Control
Set Point
P + I Bandwith
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