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How to set the Analog Out output of PCI-6251 to HiZ (high Impedance)?

Hello everyone,

Can I set the analog out of PCI-6251 to high impedance? How?
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Message 1 of 6
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Hi Jack,

The analog output impedance of the PCI-6251 is 0.2ohm per the specifications sheet, and this value cannot be changed in software.  It is typically preferred that the output impedance be as low as possible on a voltage source.  If your application calls for high source impedance, you could put an external resistance in series with the current path to increase it.  However, all this does is create a voltage divider with your load impedance; leaving out the external resistor and generating a lower voltage level would have the same effect.

Regards,
Andrew W
National Instruments
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Message 2 of 6
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Thanks for that.
 
But what I am wanting to know is when the state of the output is in High Impedance or OFF. In most cases, people misunderstood that when you set a source to 0 volts doesn't mean turning it OFF. It is still ON with an output voltage of 0 volts.
 
Being in high impedance or output OFF state would mean that the analog output of 6251 is not sourcing, even 0 volts. Take for example a Keithley sourcemeasure unit. It has a GPIB command to set the output OFF.
 
With this, is there a way to set an analog voltage output of 6251 to OFF?
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Message 3 of 6
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Would using one of your digital outputs to open a normally closed reed relay to open (disconnect) the analog output signal to your circuit suit your needs? About as high impedance as it gets.
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"It’s the questions that drive us.”
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Message 4 of 6
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Hi Jack,

There is not a way to set the analog voltage of the 6251 to OFF in the manner you describe.  The power-on state for the device will be +/-5mV, and the output cannot be set to a high impedance state.  Would the suggestion in the previous post be an option for you?

Regards,
Andrew
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Message 5 of 6
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Of course, relay is the first thing in my mind. I'm just looking into an alternative of not using relay. Thanks anyway.

Message Edited by Jack Me on 04-12-2007 08:34 PM

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