User guide

Watlow Series 97 Features ■ 5.7
Retransmit
The retransmit output can be used to transmit an analog signal representing the value of
the input process variable. The retransmit signal can be configured as either a milliamp or
a voltage signal. In choosing the type of retransmit signal the operator must take into
account the input impedance of the external device and the required signal type, either volt-
age or milliamps.
A typical application might use the retransmit option to record a process value with a chart
recorder.
Figure 5.7 — Retransmit example.
In the example a Series 96 is being used to control the temperature of a heat-treat oven and
the Series 97 is being used as a safety limit with a retransmit output. Output 4 of the
Series 97 must be equipped for retransmit (97_ _ - _ _ _ M - _ _ _ _).
The temperature of the limit process value is being recorded on a chart recorder. The oven
temperature range stays between 600 to 900°F. The chart recorder requires a 4-20mA sig-
nal.
Set [Aout] Analog Output 4 (Output 4 Menu) to [Proc] Process 1 and [Prc4] Process 4
(Output 4 Menu) to [4-20] to tag the input 1 process value as the parameter to be retrans-
mitted. Set Analog Output High [A`hi] to 900 to set the high range for the retransmit sig-
nal. Set Analog Output Low [A`Lo] to 600 to set the low range for the retransmit signal.
Set Analog Output Offset [ACAL] to 0, assuming no calibration offset is required.
The retransmit output will be 4mA until the oven temperature is greater than 600°F, at
which point the signal will increase with temperature to 20mA at 900°F and will not exceed
20mA.
Temperature Controller
Limit Controller
input 1 output 1
heater
234 %
96
1
234
LIMIT 97
1
RESET
input 1
output 1
output 4
Chart Recorder
Heat-treat Oven
limit
sensor
temperature
sensor
input 2