CMC TECHNICAL REFERENCE MANUAL
1X36003 Version 2.52
1996-1999 Ingersoll-Rand Company
Date of Issue: 18-Oct-1999
75
Automatic Starting
NOTE
Most electric motors are only rated for two cold starts or one hot start per hour. It is
the operator’s responsibility not to exceed the electric motor’s limitation. The control
system allows the compressor to be started when the compressor is ready, not the
motor.
Remote start and stop through hard wiring to the compressor control panel, communicating
through the MODBUS port via RS422/485, Auto-Hot Start and Auto-Cold Start are the four
options for automatically starting and stopping with the CMC. With each of these options a
REMOTE COMMUNICATIONS DISABLED/ENABLED or REMOTE FUNCTIONS
DISABLED/ENABLED, selector switch is provided on the device plate with a REMOTE
ENABLED light. Since each option performs basically the same function, only one should be
purchased for a single CMC. The specific method selected depends upon the application.
Remote Start and Remote Stop – Hardwired
When this option is purchased, two digital inputs are configured on the CMC Base Control
Module, one for remote start and one for remote stop.
Remote Start Digital Input
This input is driven by a momentary contact closure of at least 120 milliseconds. For the
start to proceed, the panel power must be on, the compressor must be in the Ready state
(all utilities must be running and permissive functions satisfied) and the REMOTE
FUNCTIONS DISABLED/ENABLED selector switch is in ENABLED mode prior to
energizing the input.
Remote Stop Digital Input
This input is driven by a maintained contact closure. The remote stop input is always active;
that is, the remote stop can be initiated regardless of the REMOTE FUNCTIONS
DISABLED/ENABLED selector switch position.
Communications
Remote starting and stopping can be accomplished through the MODBUS communication
port in various ways. See the section on Communications that follows for these options.
Again, panel power must be on, all utilities must be running and permissive functions
satisfied in order for the start-up to proceed.
Auto-Hot Start
Normally purchased in multiple compressor applications where backup air is required, this
automatic starting option allows the compressor to be started when the system air pressure
is below a user selected set point pressure.
Panel power must be on, all utilities must be running, the AUTO HOT START
DISABLED/ENABLED selector switch must be in the ENABLED position and all permissive
functions satisfied in order for the start-up to proceed. Solenoid water valve(s) are provided
for the intercooler(s) to reduce water consumption when the compressor is not running. A
