Watlow EZ-ZONE PM User Manual download pdf (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

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Watlow EZ-ZONE PM User Manual Page 79

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