Watlow CLS200 - Manual (Page 173)

CLS200 Series User’s Guide Chapter 8: Tuning and Control
Doc.# 0600-3050-2000 Watlow Anafaze 157
Control Outputs
The controller provides open collector outputs for control.
These outputs normally control the process using solid
state relays.
Open collector outputs can be configured to drive a serial
digital-to-analog converter (Serial DAC) which, in turn,
can provide 0 to 5 V
Î (dc), 0 to 10 V Î (dc) or 4 to 20 mA
control signals to operate field output devices.
Output Control Signals
The following sections explain the different control output
signals available.
On/Off
When on/off control is used, the output is on or off depend-
ing on the difference between the setpoint and the process
variable. PID algorithms are not used with on/off control.
The output variable is always off or on (0% or 100%).
Time Proportioning (TP)
With time proportioning outputs, the PID algorithm calcu-
lates an output between 0 and 100%, which is represented
by turning on an output for that percent of a fixed, user-se-
lected time base or cycle time.
The cycle time is the time over which the output is propor-
tioned, and it can be any value from 1 to 255 seconds. For
example, if the output is 30% and the cycle time is 10 sec-
onds, then the output will be on for 3 seconds and off for 7
seconds. Figure 8.5 shows examples of time proportioning
and distributed zero crossing (DZC) waveforms.
Figure 8.5 Time Proportioning and Distributed
Zero Crossing Waveforms
Time Proportioning (30%)
On
Off
0 3 10
Seconds
Cycle Time set to 10
Distributed Zero
0 1 3 4 6
AC Cycle
Crossing (33%)