Detecting mains into a CPU

I have a relay board that I want to test by ATE. The multiple relays switch varous things on @ 240Vac . What is a simple low power method to detect the mains outputs? Best I have is half wave,smoothed, into an opto isolator( 2 watt load resistor is the bug bear) . Is there a simpler solution? Cost is not too important. TIA.

Reply to
TTman
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Use an AC input module. Particularly for a test rig, this is the right answer.. they usually have an LED built in to show the state and sit vertically on your board saving space and provide isolation. They should cost around $10-15 each in small quantities.

You can build all that stuff on a board, maybe with a capacitive-resistive dropper and/or a sensitive AC-input opto-isolator, but why bother?

Reply to
Spehro Pefhany

How about using a small disc capacitor instead of the resistor? Be sure to put a diode across the led for reverse polarity.

Tom

Reply to
tm

You can use a "wattless dropper" capacitor with a standard opto-isolator + reverse protection diode inverse parallel with the IRLED, you still have to use a series resistor to protect the diodes from spikes and surges.

I'd suggest between 1 & 2k for the resistor, start with 0.1uF and increase until it drives the IRLED reliably.

The capacitor must be X2 class rated for continuous connection across the mains - a common component found in most equipment as mains input filters.

You could also save component count by using AC input opto-couplers (saves the reverse protection diode) but they cost more.

Reply to
ian field

He said cost is not important, right? So get a fluke 289 with the serial interface for each channel. When the job is over, hit ebay.

Reply to
tm

Are you useing a darlington output type? These typically have minumum CTR in the thousands. See.

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All you need is 0.5mA to 1mA led current .

They dont give the fastest switching times but for 50-60Hz you dont need them.

Reply to
Hammy

Why not a simple *lamp* (240VAC, low wattage) on each output sensed with a phototransistor/diode/CdS? This assumes you can't replace the 240VAC with something "more convenient" (e.g., 5VDC)

*during* ATE!
Reply to
D Yuniskis

Use inamps with high resistance dividers at the inputs. Yes, there will be a current of ~100uA from AC into your ground; that won't matter if the things are connected properly.

VLV

Reply to
Vladimir Vassilevsky

Decouple your DUT power from AC mains by 1:1 transformer. Then you can sense the power outputs directly; optocouplers not needed.

VLV

Reply to
Vladimir Vassilevsky

"TTman" kirjoitti viestissä:gyWjn.201633$ snipped-for-privacy@newsfe12.ams...

Relay with 240 Vac coil?

Reply to
E

DING DING DING DING DING! We have a winner!! :>

Reply to
D Yuniskis

Use a neon bulb coupled to some sort of photo detector. You could buy these at one time for phone ring detectors.

Reply to
qrk

What do you need to detect at 240V? Simply the presence of the voltage indicating the relay has closed? Or a voltage under load to detect bad relay contacts?

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Paul Hovnanian  paul@hovnanian.com
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Reply to
Paul Hovnanian P.E.

Yes, I think so... thx.

Reply to
TTman

Just contact closure. Post assembly testing.

Reply to
TTman

Filamanet transformer?

Reply to
krw

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Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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Reply to
Spehro Pefhany

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Neon Vactrol.

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Reply to
John Fields

They are nice !

Reply to
TTman

ch

e

Hi TTMan If all you want to test is whether the electromagnetic relays on a board are working correctly, any simple low current continuity detector (buzzer) will do fine. Is that all you need? amark

Reply to
amark

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