ABB ACH 400 User Manual page 18

Chapter 2 – Overview of ACH 400 with Electronic Bypass
Caution: The Electronic Bypass will not work properly if the relay outputs
RO1 and RO2 or the digital inputs DI1 and DI2 are reassigned by changing
ACH 400 configuration settings. The only macros that provide the proper
configuration settings are the HVAC, HVAC Floating Point and the HVAC
PID Control macros. Refer to the ACH 400 User's Manual for additional
information.
Three of the digital inputs of the ACH 400 are available for selecting constant
speeds or providing Speed Increase and Speed Decrease inputs. The functions
of these inputs is determined by the ACH 400 macro selection. Refer to the
ACH 400 User's Manual for additional information.
The ACH 400 Auto Mode External Reference input is an analog input that sets
the operating speed when the ACH 400 HVAC macro is selected and the drive
is in the Auto mode. When the HVAC PID Control macro is selected, analog
inputs are used for setting the PID reference and receiving the transducer
feedback "actual" signal. Refer to the ACH 400 User's Manual for additional
information.
The Output Frequency analog output of the ACH 400 provides a 4 to 20 mA
signal proportional to the drive output frequency or motor speed.
ACH 400 with Electronic Bypass User's Manual 2-9