Watlow EZ-ZONE PM - Manual (Page 79)

Watlow EZ-ZONE ® PM Limit Controller • 76 • Chapter 8 Features
Scale High and Scale Low
When an analog input is selected as process voltage or process current input, you must choose the value of volt-
age or current to be the low and high ends. For example, when using a 4 to 20 mA input, the scale low value
would be 4.00 mA and the scale high value would be 20.00 mA. Commonly used scale ranges are: 0 to 20 mA, 4
to 20 mA, 0 to 5V, 1 to 5V and 0 to 10V.
You can create a scale range representing other units for special applications. You can reverse scales from
high values to low values for analog input signals that have a reversed action. For example, if 50 psi causes a 4
mA signal and 10 psi causes a 20 mA signal.
Scale low and high low values do not have to match the bounds of the measurement range. These along with
range low and high provide for process scaling and can include values not measureable by the controller. Re-
gardless of scaling values, the measured value will be constrained by the electrical measurements of the hard-
ware.
Select the low and high values with Scale Low [`S;Lo] and Scale High [`S;hi]. Select the displayed range
with Range Low [`r;Lo] and Range High [`r;hi] (Setup Page, Analog Input Menu).
Range High and Range Low
With a process input, you must choose a value to represent the low and high ends of the current or volt-
age range. Choosing these values allows the controller’s display to be scaled into the actual working units of
measurement. For example, the analog input from a humidity transmitter could represent 0 to 100 percent
relative humidity as a process signal of 4 to 20 mA. Low scale would be set to 0 to represent 4 mA and high
scale set to 100 to represent 20 mA. The indication on the display would then represent percent humidity and
range from 0 to 100 percent with an input of 4 to 20 mA.
Select the low and high values with Range Low [`r;Lo] and Range High [`r;hi] (Setup Page, Analog In-
put Menu).
Outputs
Retransmitting a Process Value or Set Point
The retransmit feature allows a process output to provide an analog signal that represents the set point or
process value. The signal may serve as a remote set point for another controller or as an input for a chart re-
corder documenting system performance over time.
In choosing the type of retransmit signal the operator must take into account the input impedance of the
device to be retransmitted to and the required signal type, either voltage or milliamps.
Typically applications might use
the retransmit option to record one of
the variables with a chart recorder or
to generate a set point for other con-
trols in a multi-zone application.
Outputs 1 and 3 can be ordered
as process outputs and used to re-
transmit. Select retransmit [rMt] as
the Output Function [``Fn] (Setup
Page, Output Menu). Set the output
to volts [uoLt] or milliamps [`MA]
with Output Type [`o;ty]. Select the
signal to retransmit with Retransmit
Source [`r;Sr].
Set the range of the process output with Scale Low [`S;Lo] and Scale High [`S;hi]. Scale the retransmit
source to the process output with Range Low [`r;Lo] and Range High [`r;hi].
When the retransmit source is at the Range Low value, the retransmit output will be at its Scale Low val-
ue. When the retransmit source is at the Range High value, the retransmit output will be at its Scale High
value.
Retransmit Source
Output Scale
Range High
Range Low
Scale High Scale Low