PLC and LabVIEW interface

To regulate the operation of various control schemes, a PLC and LabVIEW-based control system is being created. LabVIEW compared to the logic of the ladder. Saving historical information in a database is also comparatively simple.

Interfacing both LabVIEW and PLC will combine the Reliability of PLC’s for control and flexibility of LabVIEW for HMI. A LabVIEW program is used for displaying PLC values to the user and allowing the user to regulate PLC elements. The PLCs are programmed to work flawlessly to detect if they lose communication with each other or the PC.

Interfacing the PLC network to LabVIEW:

The figure below illustrates the communication link between an Allen - Bradley PLC with LabVIEW:

The PLC network has a master scanner module and in a daisy chain configuration various slave “adapter” modules are linked with twisted pair.

This enables the remote PLC to be treated as memory map expansion by the master PLC. This brings some communication latency acceptable to our application. There is a limit to how many distant PLC channels we can accommodate that meet our requirements.

An OPC client I / O server can be configured in LabVIEW and a shared variable library of variables “bound” to the OPC client can be created.

LabVIEW reads a digital input to the PLC by looking directly at the Input bit in the PLC memory map.

LabVIEW turns on a digital output of the PLC by writing a 1 to a binary bit that is on the same rung as the desired output bit.

LabVIEW reads/writes analog signals by reading or writing a UINT16 in the PLC memory map.

Advantages of interfacing PLC with LabVIEW:

Attracts developers the benefit of the PLC reliability coupled with the flexibility of LabVIEW.

Good for adding various means of communication to the control scheme, such as RS232 Modbus Relay Communication or RS232 Serial Vacuum Pump Controller Communication.

PLC hardware has proven to be robust and reliable for decades. PLC’s are made to operate continuously in harsh environments for years

LabVIEW software is simple to use to create an HMI, to interact with other serial and Ethernet systems and to interface with historical databases.