Pro/Con using PLC for analog input?

[johnnie]

My company does not use our S7 300 series PLC for analog inputs.
Instead we use these:
Tesar

Staiger

I ask the engineers why not let the PLC do the work??
They say too much programming....

What are the benefits of using these instead of the PLC?
Thanks!!

 

[panic mode]

Maybe they already figured out what was meant by following

- rivers to 20mA ( current )
- Pt100-Fuehlern ( sensors )
- built in the 19"-Gehaeuse ( rack )

Ok, it could be that analog PLC card doesn't match the reqd. specs.
These seam to run much faster and have 16-bit reseolution.

 

[Mike6158]

PLC's for Process Control

We use PLC's for process control all of the time. I have one plant that has over 125 PID loops running in a single processor. Maybe your engineers haven't stepped up to the new millenium?

I justs realized that you said S7-300... That's a different issue. For one thing the 300 processor wouldn't be able to handle 125 PID loops. It does ok with 10 or so. That's the most that I've implemented in the S7 so that's all that I can speak to. FB41 is the block that we use for PID control in the S7. It's a peach. Not. You have to add code for bumpless transfer and cascade can be "interesting" to implement. Personally I think that they should give this block to their users but they don't. You have to pay for it. Typical Siemens (still love their PLC's though).

I've been trying to find the time to write my own FB but work has been a little busy of late.