Controlling the compressor via Modbus

The compressor can be monitored and controlled via Modbus.

By default the parameter "Modbus control enable" is set to "COM1", which also allows to control the compressor via digital/analogue signals if there are no commands via COM1. The commands from the different interfaces are merged, and the resulting "Control Word" can be read via the Modbus interface. The start command can be provided either by the digital input or via Modbus. The setpoint from the analogue input and Modbus are summed up. The setpoint is limited to 100%, even if the sum of setpoints may be > 100%.

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

Must be set to 1

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 to instruct the controller to accept the serial control word.

  • 0 = The serial control word as well as the serial setpoint are ignored. This means that if the start command was active just before the data valid bit is set to "0" the command remains active until the data valid bit is set to "1" and the start bit is set to "0".
  • 1 = The serial control word and serial setpoint will be accepted.

The resulting control word (102 (I)) will always have this bit set.

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

The neutral value of the control word is 43F hex (= 1087 dec = 10000111111 binary).
To start the compressor, the control word must be 47F hex (= 1151 dec = 10001111111 binary).

The actual status of the CSV can be seen in the status word (102 (I)).

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 CSV 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:

Any received Modbus telegram resets the timeout function.

Status word

The actual status of the CSV 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

Not used

1

Frequency inverter ready

The frequency inverter is ready
0 = Frequency inverter is not ready
1 = Frequency inverter is ready (mains supply is given, FI inrush is completed)

2

Operation enabled
(available with firmware versions >2.22)

0 = CSV is not ready for operation.
1 = CSV is ready to operate, but the start might be delayed by the start to start interval.

  • Frequency inverter is ready (Bit 1 = 1)
  • No fault (Bit 3 = 0)
  • No motor-off (coast) command (either via digital input DI2 if activated or Modbus)

3

Fault

0 = No fault alarm(s)
1 = A fault alarm is active. The compressor is stopped.

4 .. 5

Not used

6

Start disabled

0 = Compressor start is enabled

  • Operation enabled (Bit 2 = 1)
  • Start command given (either via digital input DI1 or Modbus)
  • Setpoint > 1 %

1 = Compressor start is disabled

7

Warning

0 = No warning alarm(s)
1 = A warning alarm is active

8

On reference

0 = The compressor is ramping or not running.
1 = The compressor is operating at setpoint.

9

Not used

10

Limiter active

0 = No limiter function is active
1 = A limiter is actively regulating the setpoint to keep the compressor in operation (reducing the risk of a fault stop)

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

  • Start enabled (Bit 6 = 0)
  • Start to start interval has expired

13

Critical

0 = No critical alarm(s)
1 = A critical alarm is active

14 .. 15

Not used