LabVIEW program for HP 4194A Impedance/Gain-Phase analyzer

[Pradipkumar]

Hey Brian,

I have been using your Labview program for the HP 4194A analyzer. I had a quick question on making impedance measurements of a device using the HP 4194A when there is a function generator connected in series with the device. From conversations I have had with Agilent, I understand that when there is a function generator or any other signal source connected in the same circuit with the analyzer, the impedance measurements cannot be trusted. Is it possible to get the analyzer to compensate for the presence of the other source. I know your LABVIEW program does some kind of instrument compensation, but does this account for the presence of other signal sources.

Your input on this would be greatly appreciated.

Pradip

[Brian_Beal]

I am not going to claim to be an expert on impedance measurements, but I will try to help.  The "open" and "short" compensations negate effects of your leads and test fixture.  It essentially measures impedance and stray capacitance at different frequencies and applies a linearized offset to the measurements for your unit under test.  You can perform the compensations with only your function generator in the circuit, and that should help.  I no longer have acces to a 4194A manual, but Agilent had a number of tech notes for the 4194A, and impedance measurements in general, on their website.  Quadtech also has some good tech notes on impedance measurements.

What kind of device are you testing?  What frequencies are you using?

[Pradipkumar]

Hey Brian

Thanks a lot for the quick reply. The device I am testing is a planar gold electrode system. Without getting into the particular details of the experiment, an AC field is applied to the electrodes using a function generator, to form "wires" between the electrodes bridging the gap. The external AC field used to form these wires are 2.5 V, 1 MHz. When the electric field is turned off, the "wires" break apart and does not contact the electrodes anymore. So the device pretty much acts as a resistive switch. I want to measure the impedance characteristics of the device when these wire form and compare it to the properties before wire formation. The HP analyzer is connected in series (OSC bias = 0.5 V) and does a frequency sweep between 100 kHz and 800 kHz. The frequency sweep done by the HP analyzer does not overlap the AC frequency applied by the function generator.

Thanks for helping me with this

Pradip

[Brian_Beal]

I have a better idea now, but I am still not real clear on what you are doing.  I think that the analyzer is essentially a function generator.  You could use the HP only, set the bias voltage to 2.5(it is AC), and either sweep or step through the 1 MHz.  The way you have it, I think that to get good readings on the HP, you would have to sweep it at frequencies at least 2 (preferably more) times the FG frequency.  Maybe you can explain why you chose 100k to 800k.

Brian

[Pradipkumar]

The "device" of interest is an active nanostructure: meaning it acts as a resistor or capacitor depending on what external AC field is applied to it. The device acts as a resistor for frequencies greater than 100 kHz and when the AC field is turned off it loses its resistive behavior. The problem is that we have to manipulate the circuit element with an external AC field (via a function generator) and simultaneously measure the circuit properties of the active nanostructure as a function of frequency using the impedance analyzer. As a result, we cannot use the HP analyzer as a function generator to manipulate the device and also do a frequency sweep to measure the properties at the same time. So durign the experiment 1) I use a external function generator to supply a constant 2.5 V, 1 MHz signal, 2) sweep between 100 kHz-800 kHz using the HP analyzer to get properties as a function of frequency. I chose this frequency range because the device behaves like a resistor in this frequency range. If I actuated from say 100 Hz - 1 kHz using the analyzer, it would change the properties of the device.

what would be a good way to make these property measurements, if it is absolutely essential for me to have another AC signal source in the same circuit as the analyzer?

Pradip

[Brian_Beal]

Again, I am not an expert on this, but whether you want it to or not, the HP is acting as a function generator.  You are superimposing the HP waveform onto the FG waveform.  This means that at some points the device will be seeing 2.0 volts or 3.0 volts

[Sulpha]

Can you use a DC 2.5 volts to activate your switch ? If so, you can use a superimposed DC bias and measure the impedance. I am not sure that there is a way where you can separate the interference of the sine function from the Imp analyzer and the constant 2MHz from your FG.

Manoj

[jdownarzap2]

Has anyone know how to READ sweep frequencies (log mode)...or can point me to a Programming Manual?

thanks

[Simran_K]

Hello,

I found the Operation Manual online and would recommend contacting Agilent regarding the programming manual. Also, have you looked at the NI Instrument Driver VIs for HP 4194A?

Thank you,

[jdownarzap2]

Thanks,

From my research (including contacting Agilent) I assume that the Programming Manual doesn´t exist back then...

Also, the driver (from NI) doesn´t contain such a function (because it wasn´t included by HP as well).