Watlow PM PLUS™ 6
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Chapter 8: Features
Ten Point Linearization
The linearization function allows a user to re-linearize a value read from an analog input. There are 10 data
points used to compensate for differences between the sensor value read (input point) and the desired value
(output point). Multiple data points enable compensa-
tion for non-linear differences between the sensor
readings and target process values over the thermal or
process system operating range. Sensor reading
differences can be caused by sensor placement,
tolerances, an inaccurate sensor or lead resistance.
The user specifies the unit of measurement and then
each data point by entering an input point value and
a corresponding output point value. Each data point
must be incrementally higher than the previous point.
The linearization function will interpolate data points
linearly in between specified data points.
Output Point 1 is the minimum value that can be displayed, and Output Point 10 is the maximum
value that can be displayed. Consider setting Output Point 1 to the minimum operating range and
Output Point 10 to the maximum operating range for that sensor type.
Output Features
Duplex
Certain systems require that a single process output, control both heating and cooling outputs. A PM
PLUS™ with a process output can function as two separate outputs. With a 4 to 20mA output the heating
output will operate from 12 to 20mA (0 to +100 percent) and the cooling output will operate from 12 to 4mA
(0 to -100 percent).
In some cases this type of output is required by the device the PM PLUS™ controls, such as a three-way
valve that opens one way with a 12 to 20mA signal and opens the other way with a 4 to 12mA signal. This
feature reduces the overall system cost using a single output to act as two outputs.
Outputs 1 and 3 can be ordered as process outputs. Select duplex as the Output Function (Setup Page,
Output Menu). Set the output to volts or milliamps with Type. Set the range of the process output with Scale
Low and Scale High.
NO-ARC Relay
A NO-ARC relay provides a significant improvement in the life of the output relay over conventional relays.
Conventional mechanical relays have an expected life of 100,000 cycles at the rated full-load current. The
shorter life for conventional relays is due to the fact that when contacts open while current is flowing metal
degradation occurs. This action produces unavoidable electrical arcing causing metal to transfer from one
contact to the other. The arcing conditions continue on each subsequent contact opening until over time the
resistance through the contacts increases causing the contacts to increase in temperature. Eventually, the
contacts will weld together and the relay remains in the on state.
The Watlow NO-ARC relay is a hybrid that uses a mechanical relay for the current load and a triac (solid-
state switch) to carry the turn-on and turn-off currents. NO-ARC relays extend the life of the relay more than
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5 6
7
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9
Reading from Sensor
without Linearization
(Actual Value)
Input Point 1
Output Point 1
Input Point 10
Output Point 10
Offset Zone
Reading from Sensor
with Linearization
(Displayed Value)
No Offset
Temperature
Time
