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Arbitary Waveform Amplitude

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Hi,

 

We were thinking of using a PXI-5421 Arbitary Waveform Generator card to generate a 50Hz 'bright-up' signal but the max amplitude of the signal needs to be +/-14V but the max avaliable amplitude from the 5421 is +/-6V, any ideas?

 

Regards

 

Steve

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The max amplitude is +/- 6V into a 50 ohm load (as the source impedance of the device is 50 ohms, to match the typical load).  But if your load is high impedance, you'll get +/- 12 V out.  Don't know if that is enough for you, but at least it's closer.

 

Neil

 

Neil Feiereisel
Principal Engineer, Modular Instruments, National Instruments
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Thanks for the reply Neil,

 

Our load will be 27KOhms, is this high impedance?

 

Regards

 

Steve

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Yes.  You'll get (27,000 / (27,000 + 50)) = 99.815% of the voltage across your load, or +/- 11.978 V.

 

Neil

 

Neil Feiereisel
Principal Engineer, Modular Instruments, National Instruments
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Neil

 

As it turns out +/-11V should be sufficient so the PXI-5421 should do the job

 

Thanks again

 

Steve

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When you get the arb and are programming it, be sure to set the Load Impedance attribute to 27,000 ohms, so the driver knows the impedance of your load.  If you don't set that attribute, it defaults to 50 ohms, and when you try to output 6 V, you would get 12 V on your load.  But when you set the attribute, and tell us to output 11.5 volts (or whatever), that's exactly what your load will see.

 

Neil

Principal Engineer

Modular Instruments

Neil Feiereisel
Principal Engineer, Modular Instruments, National Instruments
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