analog output demonstration

jmccam · May 17, 2012

I want to demonstrate an analog output signal to a tangible device other than a meter. Is is possible to connect a very small DC 12 volt motor to a 0 to 10 volt analog output from a 1763 allen bradley card? Any issues with current or noise from the motor to the module? A small 12 volt, permanent magnet hobby motor is what I want to use, speed would vary with signal. Thanks

Helliana · May 17, 2012

Look up the maximum current that the card can supply in its user manual and then check and see how much current the motor pulls.

My guess would be no.

keithkyll · May 17, 2012

Small fan for a PC (CPU cooler) might work.

joseph_e2 · May 17, 2012

How about an incandescent lamp? As long as you don't exceed the voltage rating it will get brighter/dimmer as the voltage is changed. Of course, if you do exceed the rating, it will get very bright, then very dim

Helliana · May 17, 2012

joseph_e2 said:
How about an incandescent lamp? As long as you don't exceed the voltage rating it will get brighter/dimmer as the voltage is changed. Of course, if you do exceed the rating, it will get very bright, then very dim

An incandescent lamp is going to have the same problem as a motor; It is going to draw more current than the card can supply and probably damage the card.

Look at page 27 of http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1746-in008_-en-p.pdf

Maximum Load Current is 10mA. I don't any kind of useable motor or incandescent lamp will be able to operate off 1/10 Watt.

joseph_e2 · May 17, 2012

I didn't really look up the specs on the card itself, but it was the only thing I could think of quickly. Perhaps an LED with a current limiting resistor? It's been a while since I got down to that level, but it may be possible to find one that is bright enough to see at 10mA.

An alternative would be to build an amplifier circuit that can drive enough current to do something useful.

joseph_e2 · May 17, 2012

I managed to dig out an old lab manual. We typically limited LED current to 10mA. If the output is 10V, just put at least 1k of resistance in series with the LED. In this case, I would probably start with 2k to be safe. It *should* be possible to see the brightness of the LED change as the analog output changes.

Note: I have NOT tested this. YMMV

Helliana · May 18, 2012

According the the specs, the card will support and resistance above 1000 ohms, so using a LED with a 1k or 2k resistor in series MAY work. However, i don't see it giving you the WOW factor that you are looking for.

IMO, the best thing you can do is wire the analog output to a AC drive and control the speed of a AC motor. That is one of the most common applications you students will be doing when they get in the "real world" so that would be the most beneficial if the hardware is available.

joseph_e2 · May 18, 2012

I think Helliana is right, if, as she said, the equipment is available.

Saffa · May 18, 2012

If you don't have access to a VSD, or don't want your students to be exposed to mains voltage (which might be a good thing if they're first year engineers fresh off the bus...) you could try and find something like this:

http://www.jaycar.co.nz/productView.asp?ID=KC5502

basically it's a small DC motor controller kit. you'd need to modify the circuit slightly to remove the potentiometer and maybe add a voltage divider to scale your analog output to the voltage levels the circuit would be expecting.

They'd also get to build the kitset which is always fun!

L D[AR2P#0.0] · May 18, 2012

Here's an off the wall idea, use a couple of relay contacts to alternately connect the analogue output to a capacitor, then disconnect the capacitor from the analogue output and connect it to the motor. A 3:1 mark:space ratio will match the 10mA out from the card to the 30mA no load current for the motor.

10mA for 3 secs into a 5000microfarad capacitor will give 6V

scameron81 · May 18, 2012

You could use use a 0-10V dimmable LED driver:

http://www.trcelectronics.com/roal/power-supply-rsld035.shtml

Its made for LED lights but it should work on a small DC motor.

Lancie1 · May 19, 2012

Here's an off the wall idea,

Brilliant idea, LD. It also will force some learning about capacitors, timers, and relays at the same time!

analog output demonstration

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