Controlling the compressor via Modbus

The compressor can be monitored and controlled via Modbus. In case the compressor shall be controlled via Modbus, the parameter "Control mode" must be set to "External: Modbus". While the start command and the setpoint must then be given via Modbus, the digital input "DI2 Force" can still be used to operate the frequency inverter at the configured fixed speed.

Serial control word

The serial control word is set via the Modbus holding register 110:

Parameter	Unit	Data type	Scaling	Address (I/H)	Register count
Serial control word	None	uint16		110(H)	1

Bit definition of the serial control word:

Bit	Function	Description
0 .. 2	Reserved	Should be set to 1 (for compatibility to the CSV)
3	Enable operation	Enable operation 0 = Motor-off (coast) 1 = Enabled
4 .. 5	Reserved	Must be set to 1
6	Start	Start command 0 = Stop 1 = Start active
7	Reset	Fault reset command is active when bit is set from 0 to 1. Positive edge triggered.
8 .. 9	Reserved
10	Data valid	Must be set to 1
11 .. 15	Reserved

Examples of serial control word setups:

Command	Hexadecimal value	Decimal value	Binary
			Reserved	Data valid	Reserved	Reset	Start	Reserved	Enable operat.	Reserved
Motor-off (coast)	437	1079	00000	1	00	0	0	11	0	111
No command / Stop	43F	1087	00000	1	00	0	0	11	1	111
Start	47F	1151	00000	1	00	0	1	11	1	111
Reset	4BF	1215	00000	1	00	1	0	11	1	111

To start the compressor, the control word must be 47F hex (= 1151 dec = 10001111111 binary).

Serial setpoint

The serial setpoint is set via the Modbus holding register 111:

Parameter	Unit	Data type	Scaling	Address (I/H)	Register count
Serial setpoint	%	int16	100	111(H)	1

Modbus control timeout function

If the Modbus communication is interrupted, the VARIPACK can be configured for different reactions to this interruption by the parameters "Modbus control: Timeout function" and "Modbus control: Timeout".

Configuration possibilities for the timeout function:

Fault
--> compressor stops with the fault alarm "50 Modbus control timeout"
Ramp to stop then fault
--> compressor ramps down, stops and then trips with the fault alarm "50 Modbus control timeout"
Ramp to stop (no fault)
--> compressor ramps down and stops

Any received Modbus telegram resets the timeout function.

Status word

The actual status of the VARIPACK can be seen via the Modbus input register 103.

Parameter	Unit	Data type	Scaling	Address (I/H)	Register count
Status word	None	uint16	1	103(I)	1

Status word bit definitions

Bit	Function	Description
0 .. 1	Not used
2	Operation enabled	0 = The STO input is open 1 = The STO input is closed
3	Fault	0 = No fault alarm(s) 1 = A fault alarm is active. The compressor is stopped.
4 .. 7	Not used
8	On reference	0 = The compressor is ramping or not running. 1 = The compressor is operating at setpoint.
9 .. 10	Not used
11	Running	0 = Compressor is not running 1 = Compressor is running
12	Start active	0 = Compressor start is not active 1 = Compressor start is active STO input activated (Bit 2 = 1) No fault (Bit 3 = 0) Start command given (either via digital input start or Modbus) In case "setpoint control characteristic" = "0 .. Max": setpoint > 1%
13 .. 15	Not used