Herrmidifier Herrtronic MD Engineering Guide - Manual (Page 3)

Herrtronic ® MD Series
E n g i n e e r i n g G u i d e
3 www.herrmidifier-hvac.com
Herrtronic MD: Basic Operation
Controlled humidification requires a very precise
control system. The Herrtronic MD utilizes a
microprocessor to monitor performance and
maintain humidity. Further, the Herrtronic MD
evaluates the operation and alerts the operator
to problem conditions and prevents undesirable
operation.
1. Start-Up: On initial start-up, the fill valve
opens allowing water to enter the cylinder.
When the water level rises to the electrodes,
current will flow and the water will begin
heating. As the water temperatures increases,
its conductivity also increases accelerating
the rate of temperature increase. When the
output reaches the “capacity setpoint,” the
fill valve closes. The output capacity may
continue to rise slightly beyond the “capacity setpoint.” As
the water boils, the water level falls with resulting output
reduction.
NOTE: Two conditions may occur on start-up that will alter the
normal start sequence:
A. Low Conductivity Water: Under this condition, the
output capacity may not initially achieve the “capacity
setpoint.” The water level continues to rise until it
reaches the cylinder full electrode closing the fill valve.
The unit will now cycle between cylinder full and fill
mode until a combination of temperature and mineral
concentration increases leads to “capacity setpoint”
being achieved.
B. High Drain Threshold: If the rate of output capacity
increase is exceptionally fast, the output may achieve
the high drain threshold before normal boiling reduces
the output. At this point the drain valve will open,
reducing the water level until the output reaches the
“capacity setpoint.”
2. Normal Operation: Upon achieving “capacity setpoint,”
the system begins operation in a steady state mode.
Output capacity slowly decreases until the elapsed
“cycle time” opens the fill valve to replenish the water
level until the “capacity setpoint” output is achieved. As
the mineral concentration in the water increases, the
water conductivity also increases. Accordingly, the rate of
boiling increases. Eventually, the rate of boiling reduces
the output capacity below the “low drain threshold” before
the “cycle time” initiates the fill cycle. At this point, the drain
valve opens discarding the mineral laden water, replacing
with fresh water, lowering the mineral concentration
allowing steady-state operation to resume. This steady
state operating mode continues with small increases in
water level to maintain output capacity (exposing new
electrode surface).
3. End-of-Cylinder Life: Steady state operation continues
with “fill and boil” and periodic drain cycles with ever
increasing water levels. Eventually the water level reaches
the cylinder full electrode representing the maximum
allowable water level. The system output begins to
decrease since there is no new electrode surface to
expose. If the system operates for six hours continuously
without achieving “capacity setpoint,” an “end of cylinder
life” fault will be displayed. Cylinder replacement should
occur to maintain satisfactory humidity levels.
The Herrtronic MD System is available with three (3) types
of control – (1) On/Off, (2) Proportional, (3) Proportional +
Integral – these provide “good,” “better,” “best” control.
1. On/Off – Humidity is sensed by a humidistat that provides
digital (Off/Off) input to the humidifier. Humidity varies above
and below the setpoint based on tolerance and accuracy of
the humidistat.
2. Proportional – The variation between the control input
signal and the humidity setpoint results in adjustments to
the unit output. Variations will be smaller than with “on/off”
control and will be within the control band.
3. Proportional + Integral – The P + I control simply evaluates
the actual humidity vs. desired humidity over a period of time
or integration period. The humidity difference, or offset, is
corrected by an offset correction. This correction shifts the
bandwidth up or down to attempt to eliminate the offset
condition.
High
Drain
Threshold
Capacity
Set Point
Low Drain
Threshold
Cylinder
Full
Steadily Increase
Water Level