High Voltage (480V) detection

[sacherjj]

I've been digging around and still can't find anything for this.  I'm trying to build a small logic controller that needs as some of its inputs, the state of 480V powered pumps.  There is a logic signal (24V AC) controlling the pumps, but they can and currently are running in manual mode.  The logic controller I'm building will need to work with both, so I need to sample the power to the pumps.

I'm comfortable with 120V AC sensing with opto-isolators.  A little less so with 240V.  Extremely not with 480V.  So I want to purchase the two sensors and let our electrician hook them up.  Then convert the output (whatever format) to get to logic levels, with proper isolation.  I will most likely include another opto-isolation level at this point.

However, I'm have trouble finding a ready made sensor for this.  In the Google age, the problem is usually finding the correct technical term for the item.  Does anyone know a specific term for this type of power on sensor?  Or better yet, have recommendations.

[mij59]

Hi,

Maybe you can use a current transformer relay.

[sacherjj]

I didn't think about the current detect side.  I should have, as they installed power monitoring last year as a way to determine cooling load needed. 

I know that sensors existed, but not amperage based relays.  That looks like the perfect solution.  Under $70 a sensor. 

http://www.automationdirect.com/adc/Shopping/Catalog/Sensors_-z-_Encoders/Current_Sensors_%28AC_-a-_DC%29/Current_Switches_-a-_Indicators/Single_Range_AC_Current_Operated_Switches

Thanks for the pointer.

[ejeffrey]

You could also avoid the electrical side completely and monitor the shaft rotation with something like a hall sensor or optical encoder.  That would depend on finding somewhere to mount the sensor.

[German_EE]

Some time ago Dave did a teardown of a voltage detection stick and all that was inside was a couple of CMOS chips. The electric field radiated by a live conductor was enough to change the state of a CMOS gate.

Would this work?

[Jay_Diddy_B]

Hi,

Consider this style of clip-on current transformers:

http://www.ebay.ca/itm/Non-invasive-AC-current-sensor-SCT-013-100A-max-/161017909696?pt=LH_DefaultDomain_0&hash=item257d6a51c0

Regards,

Jay_Diddy_B

[SeanB]

Just use a small 480V to 24VAC transformer, 2VA will give you enough to drive an optoisolated input on any PLC with no problem, or just use a 24VAC relay on the output to switch the input to the controller. Otherwise just use a contactor with a 480VAC coil and use the one contact.

[sacherjj]

You could also avoid the electrical side completely and monitor the shaft rotation with something like a hall sensor or optical encoder.  That would depend on finding somewhere to mount the sensor.

That is an interesting idea.  The motors are a couple meters from the controller, so that is doable.  Might wind up being the cheapest, too.

[richard.cs]

Neon lamp + photodiode? As a variant on the conventional optocoupler.

[T3sl4co1l]

I'm comfortable with 120V AC sensing with opto-isolators.  A little less so with 240V.  Extremely not with 480V.  So I want to purchase the two sensors and let our electrician hook them up.  Then convert the output (whatever format) to get to logic levels, with proper isolation.  I will most likely include another opto-isolation level at this point.

Optos are fine for 480V, as far as I know.  If you're building a circuit, just use bigger current-limiting resistors, and more of them.  Two metal/oxide film 2W resistors in series, heck, one I think is enough, so two gives you that design overhead.  Installed axially, the lead length is more than enough for creepage.

If you have ground nearby, you could even add low-clearance spark gaps, or actual MOVs or GDTs or whatever, to keep the isolation voltage down (you'd then use a resistor or two on each side of the opto, so common and differential voltages stay cool).

If you meant off-the-shelf detector modules or something like that, beats me -- I never played with PLCs and hardware.  I'm sure they're out there though.

Tim

[sacherjj]

I pulled off the coupling guard and it looks like the spline is sticking up enough to give me pulse with a metal detecting sensor.  I will be going with that first. 

I thought it would be easy to find the magnets that you hook onto a drive shaft for a few bucks.  I remember using those with aftermarket cruise control on cars in high school.  Now all cars have speed sensors to use already. 

Thanks for all the information everyone.  I'll update this thread with info as I solve it. 

[SeanB]

Simplest sensor for that is a car crank position sensor, as that has the magnet integrated into it. You just arrange it so it nearly touches the shaft and the spline will create the gap. They generate a nice voltage output that is easy to condition and which is quite resistant to noise.

[sacherjj]

Simplest sensor for that is a car crank position sensor, as that has the magnet integrated into it. You just arrange it so it nearly touches the shaft and the spline will create the gap. They generate a nice voltage output that is easy to condition and which is quite resistant to noise.

What I am planning on using is essentially that.However, mounting location is pretty tight, so I'm going to try some of the standard threaded metal sensor modules I can get for less than $20.  10-30V DC power with NPN output. 

The place where I will mount has a spline for the coupler.  So I should get a good mostly off, spline activating pulse.  Spec. sheets on them say they are good to 10kHz+, so it should be perfect for a 1770 rpm motor.  If the one I have for another project works, I'll pick up two more.

[penfold]

I know you've pretty much reached a conclusion that its best to monitor the movement of the load itself rather than the voltage...

I just thought it might be useful to add that the 480 V environment in an industrial setting is a lot more aggressive than just a scaled up 240 V type outlet, transients of all kinds, slow spikes, fast spikes, sporadic increases of voltage etc all carry a lot more energy, faster rise times etc than the equivalent in a domestic supply.  So any kind of monitoring where the voltages actually come in relatively close proximity to the electronics need a lot more consideration and one must be prepared for some very unfriendly conditions