CLS200 Series User’s Guide
Chapter 2: Installation
40
SSR
+ 5VDC
Watchdog Timer
(Terminal 1)
(Terminal 3)
TB18
+
-
Figure 2.23
— TB18 Watchdog Timer Output
Digital Inputs
All digital inputs are transistor-transistor logic (TTL) level inputs referenced to control common and
the in5V power supply of the CLS200.
When an input is connected to the controller common, the input is considered on. Otherwise, the
input is considered off. Most features that use the digital inputs can be user-configured to activate
when an input is either on or off.
In the off state, internal 10k resistors pull the digital inputs high to 5VDC with respect to the controller
common.
Table 2.6
—
Digital Inputs States and Values Stored in the Controller
STATE
VALUE
DESCRIPTION
Off
High
Open circuit
On
Low
DIgital input connected to controller common
External Switching Devices
To ensure that the inputs are reliably switched, use a switching device with the appropriate
impedances in the on and off states and do not connect the inputs to external power sources.
When off, the swiching device must provide an impedance of at least 11kΩ to ensure that the
voltage will rise to greater than 3.7VDC. When on, the switch must provide not more than 1kΩ
impedance to ensure the voltage drops below 1.3VDC.
To install a switch as a digital input, connect one lead to the common terminal on the TB50
(terminals 3 and 4) or TB18 (terminal 2). Connect the other lead to the desired digital input terminal
on the TB50 (terminals 43 to 50) or TB18 (terminals 16 to 18).
Functions Activated by Digital Inputs
Use digital inputs to activate the following functions:
• Load a job that is stored in controller memory. See
Job Select Digital Inputs on page 68
.
• Change all loops to manual mode at specified output levels. See
• Enable thermocouple short detection. See
Process Power Digital Input on page 71
.
• Restore control automatically after a failed sensor has been repaired. See
