Acquire must be in Config mode to perform these steps.
Acquire treats all Modbus clients as a flow computer. PLCs can be added by adding a flow computer.
1. Select ‘Flowcomputers…’ from the ‘Admin’ menu
The Flow Computers list will be displayed:
2. Click the ‘Add’ button
The Flow Computers setup screen will be displayed:
3. Enter the fields as follows:
| Name | This is the name or the tag name of the flowcomputer. |
| Type | The type will be “PLC”. |
| Protocol | The protocol can be either TCP or serial. This data must match the setup of the flowcomputer communications link. |
| Server 1 Connection 1 | This is the IP address of the PLC. TCP only. |
| Port | This is the TCP port used for connection 1. TCP only. |
| Server 1 Connection 2 | This is the IP address of the second connection. TCP only. |
| Port | This is the TCP port used for connection 2. TCP only. |
| Comm Port | This is the serial port that the flow computer is connected to. This option is only available for flow computers connected using Serial. |
| Speed | This is the baud rate of the serial port. It is normally set to 9600 baud or higher. This option is only available for flow computers connected using Serial. |
| Data Bits | This is the data bits of the serial port. It is normally set to 8. This option is only available for flow computers connected using Serial. |
| Stop Bits | This is the stop bits of the serial port. It is normally set to 1. This option is only available for flow computers connected using Serial. |
| Parity | This is the parity of the serial port. It is normally set to None. This option is only available for flow computers connected using Serial. |
| Address | This is the slave address of the flow computer. TCP only. |
4. If the PLC is not Duty/Standby jump to step 9
5. Tick the ‘Duty/Standby’ checkbox
6. Click the ‘Apply’ button
The flow computer will be saved and it will ask to create the standby flow computer:
7. Click the ‘Yes’ button
The standby PLC will be created:
8. Enter the details:
| Duty/Standby RTU | This is the name of the linked RTU in the Duty/Standby pair. Click the ‘Edit’ button to open its record. |
| Duty/Standby Status Field | This is the field that determines which of the two RTUs is the duty. Click the ‘Select’ button to assign the field. Note: Once the field has been allocated it will automatically be configured with a text description for the relevant Duty/Standby statuses. |
| Assume Duty/Standby Field | This is the field that Acquire will write to if it needs to assign one of the RTUs to be the master. This field is optional. |
9. Click the ‘Advanced’ tab
The Advanced settings will be displayed. In most cases these details do not need to be altered.
10. Enter the details:
| Message Timeout | This is the amount of time in milliseconds that should elapse after sending a message before raising a comms failure alarm. |
| Connection Timeout | This is the amount of time in milliseconds that should elapse after trying to establish a connection before raising a comms failure alarm. |
| Message Delay | This is a delay in milliseconds that can be introduced to each message to slow down the poll rate. It is only useful if the RTU cannot cope with a high volume of messages. |
| No of Timeouts to alarm | This is the number of timeouts that should be received before raising a comms fail alarm. |
| Use TCP Header | Use standard TCP/IP Modbus format. |
| Use CRC | Use CRC Modbus format for serial over TCP/IP. |
| Use Enron Events | Use the Enron Modbus format for archives. |
| Modicon Enabled | Use the standard Modicon Modbus format. |
11. Click the ‘Configure’ tab
The Modbus Map settings screen will be displayed:
12. Click the ‘Add’ button
Follow these instructions to add a flow computer field.
Alternatively follow these instructions to import a flow computer’s Modbus map.
13. Click the ‘Apply’ button
This will restart Modbus and make the new fields available.
14. Request the field
Follow these instructions to request the field from the PLC.