Watlow EZ-ZONE PM PID - Manual (Page 94)

Watlow EZ-ZONE ® PM PID Controller • 91 • Chapter 9 Features
Scale High and Scale Low (cont.)
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).
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 compensation for non-linear differences between the sensor read-
ings and target process values over the
thermal or process system operating range.
Sensor reading differences can be caused
by sensor placement, tolerances, an inaccu-
rate sensor or lead resistance.
The user specifies the unit of measure-
ment 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 previ-
ous point. The linerization function will
interpolate data points linearly in between
specified data points.
Note:
Output Point 1 will be the minimum
value that can be displayed, and Output
Point 10 will be the maximum value that can be displayed. Consider setting Output Point 1 to the mini-
mum operating range, and Output Point 10 to the maximum operating range; for that sensor type.
Outputs
Duplex
Certain systems require that a single process output control both heating and cooling outputs. An EZ-ZONE
PM controller 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 cool-
ing output will operate from 12 to 4mA (0 to -100 percent).
In some cases this type of output is required by the device that the EZ-ZONE PM 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 sig-
nal. This feature reduces the overall system cost by using a single output to act as two outputs.
2
3
4
5 6
7
8
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
T
emperature
Time