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Hewlett-Packard 1110A/1111A Current Probe & Amplifier

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  • Hewlett-Packard 1110A/1111A Current Probe & Amplifier

    I was discussing this somewhat Vintage HP 1110A Current Probe and it's matching Probe amplifier the 1111A with eschertron, but found I couldn't find any proper photos of it on the internet. I have a pair of their probes, which work as well as the Tektronix P6021 AC Current Probe (with it's type 134 Probe Amplifier). The probe also works just fine and in calibration when connected to the current probe inputs on my Tektronix R5031 dual beam scope.

    I used to use the probe connected thru the scope, with the output of that channel feeding a phase meter so I could plot impedance vs phase on capacitors when I was in the process of selecting capacitors for replacing the dip-tantalum caps on one of the three Trident A-Range Recording Consoles at Cherokee Recording Studios back in the early 80's. Looking at the impedance magnitude & phase, you can see quickly where the capacitors go non-linear. Big time with electrolytic's. Space was a problem on those console modules, but I did end up having caps made for us that had decent HF linearity. The phase plot is a way of looking at the dissipation factor in the frequency domain.

    HP produced an Application Note years ago, which I've attached here, along with their HP Journal Article when they released the 1110A/1111A Current Probe & Amplifier to the market. My probes are tucked away in my scope probe box at CenterStaging, not yet accessible due to the Covid 19 Pandemic, though I might find some catalog images in my older HP books. If I find something in there, I'll add that to the thread.

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    HP 1110A-1111A Current Probe System.pdf
    AN 157 Low Freq Gain-Phase measurements.pdf
    HP 1110A Current Probe.pdf.pdf
    HP 1111A Operating & Service.pdf

    On Page 17 of the AN157 Low Frequency Gain/Phase Measurements using a log sweep generator and the HP 3575A Gain Phase Meter, they discuss some very revealing methods of showing how different capacitor dielectrics behave over the wide frequency range. That meter has been a joy to have in my lab assets over the years. I had forgotten about this app note until I moved my technical library home, and found it in my HP 3570A Network Analyzer manual.

    In the 1110A manual, they show a graph which displays the maximum undistorted current response in terms of Amps Pk-Pk. What they don't show is the linearity of the probe at low AC current. Running in the 1mA-50mA current range, it is very flat, down to at less than 10Hz (-3dB), if memory serves. Driving the probe with an oscillator, you can inject signal current into amplifier circuits, and do Bode Plots for that matter. I think I paid $4 each for the pair I bought, leaving several in the box at Industrial Liquidators in Hawthorne, back in the mid-70's.

    One of the adapter cables I've used over the years is an AC Mains cable (Male/Female) with an IN-LINE splice where I inserted 10 smaller AWG wires in the AC Hot Line, allowing the probe to measure AC Mains Current as a 10:1 Divider, or 5:1 using two of the 10 wires with the probe clipped around them.
    Last edited by nevetslab; 04-28-2020, 05:32 PM.
    Logic is an organized way of going wrong with confidence