Mini PLC with analogue input

What are you planning to use it for?

A process signal in the range 0-10VDC is input to the controller. The controller compares the input signal against a high setpoint and a low setpoint. If the input is below the low setpoint, a relay output energises. If the input is between the low and high setpoint, the relay is de-energised. If the input is greater than the high setpoint, the relay energises.

The response of the relay should be time delayed (between 0 and 5 seconds) to prevent temporary changes in the input affecting the output.

I would have to program the controller so that the setpoints and time delay could be adjusted from the front panel using a LCD display.

The power supply needs to be 24VDC.

You can get dedicated setpoint/temperature controllers (Omron/Redlion to name but two) that do this for you without all the faff.

Oh - if you insist on using a sledgehammer to crack a nut then the Mitsi is the most straightforward. I've no experience with the IDEC but its name sounds much more like what you need....

Right. Thats the sort of thing I would have done with a quad opamp, 6 resistors and a capacitor.

Thanks, but I don't really want a setpoint controller. The dedicated product I require is a trip amplifier with user-adjustable setpoints and response time.

I'd still have a look at process controllers - you may find that someone does what you want without any programming (plenty of industrial processes out there that work in a similar way, and they don't wany Joe operator messing about with a PLC....)

Indeed. Personally, I would also use hysteresis, rather than time delay to avoid cycling.

Christian.

The message from snipped-for-privacy@boltblue.com contains these words:

Make your own with a PIC.

What are you controlling? A cylinder?

It might be a cube, or a pyramid. These are easier as they don't roll away. A sphere is a real bugger to control.

MBQ

And don't have independantly-adjustable Lower and Upper trip points.... otherwise they can be crossed over, so that the Upper is lower than the Lower.

Better to have (say) a Lower trip setting and a Window size setting, plus a clamp so that Lower+Window does not exceed 10V.

Note: The OP has a similar thread in sci.electronics.design.

Yeah, I tried to post the same thread to more than one group in Google Groups ("separate multiple groups with commas") but it didn't work for me. Don't know if you have to have a space either side of the comma or something...

So I had to rewrite my post and put it in sci.electronics.design

Not very neat but there you go.

How about installing a decent newsreader BEFORE attempting electronic design?

Like me he could just use Outlook Express. His ISP Nildram seem to have a newsfeed so really no excuse!

Another one for your list is the Crouzet Millennium range. I have used these - both their mains and 24V volt range for various control projects including domestic (heating, lights, ventilation etc). Very easy to program. I don't have any specific info on the performance of the ADC (only available on the 24V version) but their UK office are very helpful with advice. see

Chris