Can't decide on an HMI from Siemens

[MustangDan]

Please excuse my ignorance, I'm relatively new to PLC and HMI programming.

I have been given the task of monitoring twelve (12) analog signals with a Siemens S7-200 PLC. This PLC is to be connected to a touchscreen. The operator will impose four (4) limits on each analog signal - a hi/lo WARNING level, and a hi/lo ALARM level. In addition to the standard "attention-getter" light, the operator needs to be able to discern which analog signal caused the warning or alarm, and whether it was too high, or too low.

My local Siemens salesman tells me that if I need the alarm to remain after the condition has gone away, I need a memory buffer in the HMI. In the realm of 6" Siemens touchscreens, this means I need a TP170B, when I was hoping to use either a TP070 or TP170A (about half the price).

Can anyone offer suggestions of how to do the alarms and warnings on the lower level touchpanels?

Thanks alot,
Dan

 

[Skogsgurra]

"My local Siemens salesman tells me that if I need the alarm to remain after the condition has gone away, I need a memory buffer in the HMI"

It sounds like your local Siemens salesman knows less than you do - or he wants a better sale. If you are working with an S7, there should be some memory in it where you can keep flags (Merker) that get set by the fault condition and remain set when the fault is gone. Let the flag activate your visual "attention-getter" and arrange a reset button to extinguish it. This is really a very low-end application and you should not need a fancy panel.

 

[xyzz]

Skogsgurra is right.
Leave all the logic to PLC and use a touchscreen as a pure input/output console.
This is the most straightforward and cost effective solution.

 

[MustangDan]

Thanks for the responses skogsgurra and xyzz. After speaking to a Siemens tech support guru, he agreed that fault messages could be stored in V-memory. Then, I will define a message display on the HMI to look at a blank V-memory location. When a fault occurs, I will write the appropriate message from the "storage" V-memory location to the "displayed" V-memory location. Clearing the fault will clear the "displayed" V-memory location.

Thanks again,
Dan

 

[PierreR]

MustangDan,
skogsgurra and xyzz are absolutly right, keep the logic in the PLC. Just make sure you have enough memory in the CPU to do the job. Keep in mind of future expansions, you may want to buy bigger now if you have plans, rather than change in a year.

Only the text message should be and the bits for its attribute should be in the display. The acknowledgment and reset conditions come from the PLC. make sure you either have a key from the display going back to the PLC or an external PB going to the PLC.

However, be prepared to do some programming. A careful alarm system description or "requirements" planning will help your programming.

I worked with Siemens stuff for 16 years. They can do it, but if you're not carefull, it will cost you time and money.