Pulsafeeder Pulsa Series Pulsamatic Controls - Manual (Page 10)

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Operation of the second limit switch (the one closest to the circuit board) may be checked in a
similar manner. The limit switch should be open at a stroke indicator reading between 001 and
000.
If either of the limit switches appears to be out of adjustment refer to “repairs- Limit Switch
Adjustment”.
Barring any problems proceed with “Calibrations and Adjustments”.
Refer also to the “Equipment Startup” section of the pump Installation, Operation, and
Maintenance Instructions.
5. Calibration
As stated previously, field recalibration is required upon startup. The following procures are to be
performed in sequence as presented. Refer to Figure 4 as required for circuit component locations.
5.1 Deadband Adjustment
With pump stroke positioned exactly as commanded by the input signal, a certain change in signal
must occur in either direction (increase or decrease) in order to cause the actuator to respond.
For example, if a pump is operating at 50% stroke in response to a 50% input signal, the signal
must typically increase to 51% or decrease to 49% before the actuator does not respond, or is
“dead”, is called “deadband”. If deadband is too narrow, the actuator will frequently make slight
adjustments in response o small signal variations. In the extreme case, the actuator will continually
“hunt” back and forth over a small range of adjustment. If deadband is too broad, response will lag
and accuracy will suffer. The “Null” potentiometer near the center of the circuit board adjusts
deadband. Clockwise movement decreases deadband, increasing sensitivity. Counterclockwise
movement increases deadband, decreasing sensitivity.
Deadband adjustment for response to a 1% change in signal (depicted in the example above) is
appropriate to most installations. This can be set approximately by setting the “Null”
potentiometer in the six o’clock position shown in Figure 4. To check deadband adjustment, cycle
the pump automatically, by input signal command, to an approximately midrange stroke setting.
Leaving the override switch in the “in” or automatic position, slowly adjust the handwheel in
either direction until the actuator responds to return the stroke to the original set point. Care must
be taken during this operation, as the handwheel will move without warning. Deadband is
observed on the mechanical stroke indicator as the difference between the original stroke setting
and that at which the actuator responds.
5.2 Circuit Board Calibration
The PULSAmatic circuit senses all control signals in terms of voltage. A current signal is
converted to a voltage signal measured across a resistor, provided in the circuit board, through
which the current passes. For example, the most commons signal, 4-20 mA DC, passes through a
470 ohm resistor to generate a 1.88-9.40 volt DC signal, (0-6.3 v with Ratio Control).
This procedure trims the actuator circuits to the low and high ends of the actual input control
signal.