I have a Twido compact 24 controller, and a Pro-Face ST400 HMI. Being new to this whole thing, which one should I have set up as the master, and which one should be the slave? The HMI will be used to set up motor speed for pumps, using Altivar 31 drives, setting dispense times for a liquid solution, conveyor on/off control, etc. I am confused as to whether the HMI should be slave, receiving requests for data from the PLC, or the other way around.

 

HMI must be the Modbus Master. Twido port a slave Modbus

 

Hi there, John, do you have experience with Pro-Face LT3000 series? I am using external I/O driver module with 2 analog inputs. Currently I wish to collect the analog data and store it in USB storage device, hence to plot the graph in PC. Do you have any ideas for doing this? Thanks for helping.

From,
Newbie

 

The Master will be the one that decides which tags to poll, how often to poll, and when to send messages off of the regular schedule. Generally, the boss.

In your circumstance, which is common, that's the HMI. If you were doing something a little more exotic like having Modbus units remotely dial-in to your HMI to tell it of a failure or alarm condition, you'd need to have the units running in Master mode and your HMI as slave.

Adriel Michaud
MatrikonOPC