VersaPro Temperature Controller
Page 15
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Deadband allows the process to deviate away from the setpoint by the width of the deadband before any
control action occurs. The deadband is adjusted through the Proportional Band in units of the displayed
setpoint value. The reset and rate values have no effect in ON/OFF control.
Let’s assume the process setpoint is 1500° with a proportional band of 5. This represents a deadband of 5°,
which is a band of ±5° around setpoint. The hysteresis is 1° of the setpoint or 20% of the deadband. The
output is turned on when the process drops below 1495° and turns off then it reaches 1499°.
The deadband controls the point where the control is turned on to correct any deviation from setpoint. The
hysteresis controls the point where the control is turned off to prevent overshoot or chatter.
6.6
ON/OFF Dual (OD)
This mode is similar to the time proportioning dual mode. The forward output acts as described in the ON/OFF
description above. The reverse output responds when the process is above the setpoint.
Using the temperature example with a proportional band (deadband) of 5, the heat contact would turn on when
the process is 1495° and will turn off when it comes to 1499°. Likewise the cool contact would turn on when
the process exceeds 1505° and will turn off when it drops to 1501°.
6.7
ON/OFF with Complement (OC)
This mode is exactly like ON/OFF control with the addition of a second control output. The second control
contact is turned ON when the first is control contact is OFF and vice versa.
6.8
Direct Current Output
The Versapro has two analog output channels that provide an isolated 4 to 20mA signal proportional to
selectable process values. The analog outputs can be configured to control the process by driving actuators
with a 4-20mA signal proportional to the calculated percent output of the PID loop. One or both output
channels can be used depending on the control mode selected. POUT selection drives the output signal
based on the HIPO and LOPO settings. If a Dual Time Proportioning control mode is selected with a HIPO =
100 and a LOPO = -100 then the output will be 4mA for –100%, 12mA for 0%, and 20mA for +100% output.
This setting is helpful if one actuator is driving two valves in a split configuration where air is fully opened at –
100% and gas is fully opened at +100% or both are closed at 0%.
It is possible to drive two actuators independently by setting on output to PO1 or PO2 where PO1 is the 0 to
+100% control output and PO2 is 0 to –100%. In this configuration both outputs are at the maximum (±100%)
with an output of 20mA.
It is also possible to drive one actuator with an output channel and a solenoid with a control contact. For
example, select PO1 for one analog output channel to drive a gas actuator and connect an air solenoid to the
reverse control contact. The percent output for both functions is determined by the PID settings. The cycle
time should be set to the stroke time required to fully open the actuator from a fully closed condition. Typical
stroke times would be 30 to 45 seconds.
The control contacts will still act as described in the previous modes even if the analog output channels are
being used.
