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Chapter 9—C445 Logic Engine and Expansion I/O
178
Power Xpert C445 Global Motor Management Relay
MN042003EN—January 2019
www.eaton.com
In the following example, a proportional integral controller (PIC) is used to regulate the
temperature of a liquid. The temperature is measured using an ELC-TC04ANN
thermocouple module connected to the MEASVAL of the PIC controller acting as the
feedback. The heater is turned ON/OFF using the Y0 relay output of ELC-EX16NNDR.
The reference temperature is input from a potentiometer. The REFSCALE function
converts the 0 to 2000 count analog input range of the analog input to engineering units
of 0 to 500 degrees in 0.1 degree increments. The REFSCALE output is connected to the
SETPOINT of the PIC controller. The PIC function block in the program compares the
reference temperature to that of the thermocouple input. The error is applied to the PIC
equation, and the output of the PIC is used as the ON time of a MONOSTABLE timer. The
MONOSTABLE is retriggered by a retentive timer that is triggered at a fixed rate, which is
used as the period for the MONOSTABLE. This results in efficient PWM control of the
heater temperature. In a real-world application, an ELC module with a transistor output
module could be used to control a solid-state relay (SSR). Substitution of a transistor
output module and SSR for the relay module will result in greater reliability and longer life.
Potentiometer
Thermocouple
Heater