Machine Expert HVAC, M172 - Permanent on contact, Flasher Unit, and Analogue input issues

[MacsEngineer]

I am making a program to control an automatic bollard installation, and I have hit a few small roadblocks.

1. I need a constantly on contact that turns on when the PLC starts. I had a quick google and found this

 (1) Solved: M172 plc system bit - Schneider Electric Community but I am not sure what I am doing with ST as I have never used it.

2. I need a 1 second flasher unit, if there is a pre-made function block that would be much easier, but I can make my own if I can get a constantly on contact to work.

3. I am having trouble getting analogue inputs to be assigned to a ladder contact. AI5-AI8 are set as 1=DI in the BIOS settings, and it is registering as that in the commissioning tab, but when I try to apply one of the inputs to a ladder contact it says only BOOL inputs can be used. Would it work in FBD instead?

This is the first time we have used the M172 PLC and HVAC software, so any help would be appreciated.

[FedericoM · Accepted solution]

Hi,

about your points:

1. define the output DOstart you need to be swiched on at boot in the Configuration Perspective.

Create a program to be assigned to Init Task and write 

DOstart := TRUE;

2. sysTimer is a ms counter, you can get the flasher with this formula:

x1Sec := TO_BOOL((sysTimer/1000) MOD 2);

3. It would be easier in FBD, you can convert to BOOL your AI input usint the TO_BOOL.

Another option is a small ST program assigned to Timed task in which you write:

xAI5asDI := TO_BOOL(iAI5input);

...

xAI8asDI := TO_BOOL(iAI5input);

In the Ladder code you can use xAI5asDI ... xAI8asDI 

[MacsEngineer]

Thanks for the response. I have done the conversion in point 3, but for the constant on and flasher unit I am getting the "object not found" error. also, how would I refence these elsewhere in the program? would it be xDOStart and x1Sec?

I think I have sorted it. DOStart and x1Sec were not something I had created, assigning the variables I want in their place seems to be working