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Ext Trigger Input, Safe Limits

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Ext Trigger Input, Safe Limits

Postby MeridenJohn » Thu Feb 28, 2013 2:09 pm

I was wondering how to safely interpret the External Trigger voltage specifications.

The 3206B Ext Trigger Spec is +/- 5v (active) and +/-100 Volt overvoltage.

Often "overvoltage" specifications suggest some limited occurance criteria. Is this the case with the 3206B?

We are in a 0 to 20 Volt environment. We often wish to trigger on 16 volt rising edges. Is this a "safe" operating condition for repeated use?

Thanks

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Re: Ext Trigger Input, Safe Limits

Postby Martyn » Thu Feb 28, 2013 2:26 pm

The input range for the ext trigger is +/-5V, operating voltages must always be be within this range as there is no circuitry inside to step down higher voltages. The overvoltage protection means that if you accidentally put in voltages up to +/-100V you will not damage the scope.

If you wish to trigger on voltages in the +/-20V range you will need to use one of the channels on the scope and set a suitable range, or externally attenuate the voltage so that it is within the +/-5V ext input range.
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Re: Ext Trigger Input, Safe Limits

Postby MeridenJohn » Thu Feb 28, 2013 2:56 pm

Martyn,

thanks for the fast response. I would ask for one bit of further clarification.

Our application will work if triggering on a voltage below 5V. Say TTL levels. However the voltage will continue to rise to 16V or so before it stabilizes.

Basically we are triggering on the edge of the power supply being switched on. We wish to measure pressure and current on CH A and CH B.

If I make a clipping circuit to limit the power supply voltage to 5V where it enters the trigger input I would be fine....except if the ground for the trigger circuit is not connected (in error or a wire becomes undone) I would still get 16V into the external trigger input.

Thanks

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Re: Ext Trigger Input, Safe Limits

Postby Martyn » Thu Feb 28, 2013 3:00 pm

16V wont harm the device, even if repeatedly applied. If the rise to 16V is quick then the trigger time may be a bit sluggish due to saturation but it will still work. Adding a clipping circuit would be a sensible move.
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Re: Ext Trigger Input, Safe Limits

Postby MeridenJohn » Thu Feb 28, 2013 3:03 pm

Martyn

Thanks again for a fast response.

I will add a clipping circuit but now I won't worry about damage if we loose the clipping circuit ground.

Thanks

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