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"Smart Relay" with analogue input

I am looking for a microcontroller solution to the following application:

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.

I have looked at the following models: Siemens Logo Telemecanique Zelio Logic Controller IDEC SmartRelay Mitsubishi Alpha

I think all of the above would suit my purpose but I wondered if anybody had any experience with the A-to-D conversion on any of those models? Or perhaps could suggest a better controller not listed?

I'm a complete novice in the microcontroller field and would appreciate any comments. Thanks.

Reply to
denbigh1974
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I have built two versions of microcontroller based relays that would do what you require.

The first, called VRLY, is in an octal relay can and has two DPDT solid state relays. It is designed to detect two ranges of input voltage, and is self-powered from 80 to 280 VAC. The capacitor voltage dropper caused problems as noted in a previous post, but the circuit could easily be adapted to 12 VDC or 24 VDC (as it is for a different application). It has some time delay built into the software. It uses an 8 pin PIC12f675.

The other device, called a POD (Programmable Overload Device) monitors two AC input currents, and detects imbalance as well as overload, for which it provides a simulated thermal overload curve to trip a relay after a certain period of time, and closes the relay only after a proper "cooling" period, to enforce proper duty cycle overloads. It also has an input for a thermistor (1000 ohms), which also figures into the overload equation, and a filtered PWM output indicating the "virtual temperature". This is on a PC board in a small DIN enclosure with 10 screw connections. Another version of this device adds outputs to drive three LEDs, Green, Yellow, and Red, which provide an indication of both the input current and the virtual temperature.

If either of these units will meet your needs, I might be able to supply you with PC boards and PIC code, but as they were developed for the company I work for

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they would need to approve the release of the proprietary design information. The electrical design of the PC board should be no problem, and we could probably sell them to you for about $20 each or so, but the PIC code might be more sensitive. We might be able to modify the design for your needs and build them for a negotiated cost, depending on specifications and quantity.

Please contact me if you are interested.

Paul

Reply to
Paul E. Schoen

I believe you can buy these off the shelf. That is always your best solution as it avoids the maintenance costs of any sort of custom design.

Reply to
Homer J Simpson

your looking for a PLC with Analog input that will work with an existing data highway (DH) with AB or maybe something like a little Keyence PCL with analog input ? Keyence has some nice LCD screens that work nice with that also and they operate on 24 volts.

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look there.

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Reply to
Jamie

It would be good to buy an off-the-shelf solution, agreed. I found this:

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but it doesn't appear to be CE marked and I need that for use in Europe.

I did have a good look around but have unable to find an acceptable alternative, unfortunately.

Reply to
denbigh1974

Thanks for that, Paul. I'll bear that possible solution in mind.

Reply to
denbigh1974

You have posted this same thing to both sci.engr.control and sci.electronics.design. Please look up the Wikipedia entry for "cross posting" and see what it has to say about multiple- vs. cross-posting.

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Wescott Design Services
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Reply to
Tim Wescott

What about control companies like Robertshaw and Honeywell?

Reply to
Homer J Simpson

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