Old School – The XY Recorder

While working in an undergraduate plasma laboratory I had the opportunity to use an old device for recording data. The XY recorder is to data collection as the typewriter is to a computer. An ink pen is attached to a rail that moves according to input signals. The recorded takes a voltage input for both the X axis and the Y axis.

HP 7035B X-Y Recorder

Working setup of an HP 7035B X-Y Recorder.

This seemingly outdated recorder works very well in the lab. A swept Langmuir probe trace is (almost) easily acquired using a capacitor circuit to control a slowly decreasing probe potential. The image below is the result of about an hour’s worth of swept probe traces.

It should be noted that the image below shows incorrect usage of the recorder. The horizontal lines at the top of the sheet, traces 12 and 13, are the result of setting the Y range such that the recorder is off scale for most of the X values. This might cause the motors that move the pen to burn out, so it is not advised to employ such settings. This does produce the best traces, unfortunately.

sample trace from xy recorder

Sample trace from the x-y recorder.

If this data were intended for a publication, then one would have to use graph paper instead of blank paper and unplug the probe to trace out a zero signal line for calibration. It is not certain that a peer-reviewed journal would accept data acquired with a recorder. There is nothing intrinsically wrong with the xy recorder concept. One difficulty in using this method is that it works slowly and requires a lot of maintenance to keep the traces calibrated and useful.

A recorder just like this one recently finished its auction on Ebay.com. There were zero bids for the $10 initial asking price. The shipping estimate was $35 so it might not turn out to be a good deal. I tried to find out when this machine was made, but the only references to it are for purchasing old manuals and parts. If all goes well in the lab, then there will be a few more recorders on the market very soon.

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