Thank you. For those who are interested, some more details. The system has to regulate 2 vacuum pumps & do some logging:
- User interface (display & buttons. Touchscreen is not recommended here as the operators can work with sticky materials!)
- 2 analog inputs for measuring pressure
- 5 temperature inputs (tell me, what is the difference between PT100 and a simple 0..5 Volt sensor?)
- A couple of digital inputs for pump alarms, failure indicators and such
- 2 relays (with hardware soft-start) to activate the pumps
- Counting down time for pump maintenance
- Some more digital outputs to drive status LED's
- Data-log capabilities (client prefers USB stick)
- Optional, Wireless communication so that a PC can monitor, log and adjust setpoints
So far I had these two options in mind; Arduino versus Unitronics (PLC):
Arduino
- Arduino Mega
- Intelligent LCD (Demmel, anyone experience?)
- Realtime Clock (for log & maintenance messageS)these are not in by default, right?
- Optional, XBee shield for communication with a PC.
- Protection box / panel...
- Cost ~ Don't know about the protection part, but the hardware components all together
probably make a price somewhere around 350 euro. Add some more if you want XBee shield + antenna.
About the ILCD, that Demmel
http://www.demmel.com/ilcd/english/panel2412.htm
can be partially programmed so that you don't have to do all store/execute all graphics on the Arduino.
It is a touchscreen though, so you are probably paying more for something we don't really want. Anyone knows such displays
with good old robust buttons?
About logging...
http://www.antratek.nl/Memory-interfacing.html
Would that work? I noticed that most PLC's use SD cards instead. I don't really like SD, but I can imagine
it's a more robust storage device. However, I guess the client only logs small sessions on a stick than
immidiatly places it on his computer. Log-per-job.
I wonder if all those components(LCD, Logger, XBee) fit without problems on a Mega. guess so, but I could be wrong.
Plus we shouldn't forget that assembling the whole thing also takes a few manhours (= also costs).
Unitronics Vision120 HMI & LCD in one
http://www.unitronics.com/series.aspx?page=120
- Small 2 color screen with buttons
- Can write logs on a SD card
- Extra options such as SMS Alert, Ethernet or CANbus
- Cost? Those bastards always claim to be the cheapest but never gave prices. I expect the price to be between 500 and 900 euro. As far as I know, Unitronics is relative cheap compared to the real big boys.
Although logging may be kind of soggy, this solution will work. But for a higher price of course.
Another question comes up... If a PLC crashes after 5 years of operation, getting a new one (same model) is usually not
much of a problem. Would that also count for Microcontrollers, or do they change the models continuously? I know that's
hard to answer for a young company like Arduino, but it's pretty important nevertheless.