Specifications

Digital I/O Functions and Manual Mode 6-5
LIMIT SWITCHES
Two of the Manual Modes allow the use of limit switches or other external
digital signals to limit the analog output that may be obtained with the Analog
Output (AO) command. The limit switch mode may be programmed to
accommodate either normally-open (NO) switches or normally-closed (NC)
switches. See the Setup section for mode selection details.
Figure 6.4 shows a typical module with normally-open limit switches. If the
switches remain open, module operation is not affected. If the Down Limit
switch is closed, an attempt to decrease the analog output signal with the AO
command will result in a LIMIT ERROR message and the command will be
aborted. An AO command to increase the analog output will be performed
normally. As long as the Down Limit switch is closed, the analog output
cannot be decreased from its present value with an AO command.
Conversely, if the Down Limit switch is open and the UP Limit switch is
closed, an attempt to increase the analog output with the AO command will
result in a LIMIT ERROR. The output may be decreased with no error.
If both limit switches are closed, any attempt to use the AO command will
result in a LIMIT ERROR.
Figure 6.4 Using Switches to Limit Analog Output.
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