Setpoints
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MXD70 Setpoints, Current Outputs, and
Digital Inputs Configuration Guide
Setpoints
Setpoint Proportional Mode
In addition to On/Off mode the MXD70 Series also provides two forms of pseudo proportional control,
which can be used to control the levels to a defined value when used in conjunction with a pump or
valve. When the reading deviates from the programmed set point level the relay pulses at a rate
proportional to that deviation. Note – Only available when Setpoint Trigger is set to either High or Low.
Pulse Proportional Mode
The Pulse Proportional mode is intended to drive solenoid type dosing pumps which have the facility
to accept an external pulse input. The setpoint relay operates by producing a pulse of 0.2 seconds in
duration and with a maximum period of one pulse per 30 seconds. The pulse rate increases as the
measurement moves further from the set point, until it reaches the minimum period of one pulse per
0.4 seconds at the limit of the proportional band.
For example if the user sets a proportional band of 1.00, the setpoint trigger to LOW, and a setpoint
value of 10.00. When the reading falls just below 10.00 the setpoint will begin to pulse at its longest
period of once per 30 seconds. As the reading falls further from the setpoint the period will decrease
until it reaches its minimum of one pulse every 0.4 seconds at the limit of the proportional band. (See
Setpoint Pulse Rate – Pulse Proportional Mode section on the diagram below.)
Time Proportional Mode
Time Proportional Mode allows a user defined cycle time to control any on/off device such as a
solenoid valve or dosing pump over a user set proportional band.
For example if the user sets a proportional band of 1.00, the setpoint trigger to LOW, and a setpoint
value of 10.00. When the reading falls below 9.00 the setpoint would be energised 100% of the cycle
time. As the input rises and approaches the set point the setpoint starts to cycle on and off with the on
time reducing and the off time increasing, respectively until it reached the setpoint and would be off
for 100% of the cycle time. The cycle time is adjustable and is the sum of the on and off times. (See
Setpoint Cycle Time – Time Proportional Mode section on the diagram below.)
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