Watlow F4T User Manual

Watlow F4T • 72 • Chapter 4 Application Examples
Safety Limit
In this example one thermocouple measures the temperature of the chamber or oven provid-
ing feedback to a control loop that drives a heater with its heat output. A second thermocou-
ple connected to Temperature Input 1 on module 3 also measures the temperature but pro-
vides its signal to the limit function. The limit controls a form A relay output that is energized
when the temperature has not exceeded the safety limit setting and opens when the limit is
exceeded. The control loop’s output signal to the heater goes through the limit relay such that
power to the heater is cut off when the temperature is above the limit. Also a momentary
switch is connected to digital input 2 on module 3 so that the limit can be reset without using
the controller interface.
Function Block Diagram
Application Tips:
• Because the limit option is designed for safety, the limit block is automatically present
on the diagram, and its input and output signals cannot be changed.
• The signal from the digital input to the RST on the limit block allows a momentary
switch wired to that input to reset the limit alarm.

Watlow F4T Specifications

General

Inputs	Thermocouple, RTD, mA, V
Outputs	Relay, SSR, mA, V
Communication	Ethernet, Modbus RTU
Data Logging	Yes
Certifications	CE, UL, cUL, RoHS
Control Modes	PID, On/Off
Power Supply	100 to 240 VAC
Operating Temperature	0 to 50°C
Enclosure Rating	IP65
Display	4.3 in. (109 mm) color touch panel LCD
Control Loops	Up to 4