Winner, Name that Ware September 2017

The Ware for September 2017 is a WP 5007 Electrometer. I’ll give this one to Ingo, for the first mention of an electrometer. Congrats, email me for your prize! And @zebonaut, agreed, polystyrene caps FTW :)

2 Responses to “Winner, Name that Ware September 2017”

  1. Christian Vogel says:

    As the ware was submitted by me, please let me add a few explanations:

    The ware is the current sensing amplifier module from an old WP 5006 (or similar) multi channel electrometer (e.g. [1]). It is used in dosimetry [2], that is measurement of the dose of ionizing radiation, in radiation therapy such as cancer treatment. The specific device is quite old, from times when people were still using analog recorders and X/Y plotters (up to the late 80s, I would say).

    It takes the signal of a dosimery diode (used similar to a photodiode in photovoltaic mode) or an ionization chamber [3] and it takes a current in the range of few pA and converts it to a voltage in the 10V range.

    Some Ionization chambers have the collecting terminal and hence the amplifier circuit at an elevated potential (typically, say, 300V). This is why the whole circuit is galvanically isolated.

    It is pretty much your schoolbook-current-to-voltage opamp circuit, but with a lot of care taken for your feedback components (the said polystyrene caps and 10GOhm resistors) and minimization of leakage.

    The design is single ended but using two different feedback paths through the 10G resistors, the reed-contacts shown switch-in the lower-sensitivity networks onto the summing junction (the input) when a lower-sensitity range is chosen.

    [1] http://medused.com/ProductDesc.aspx?code=51656

    [2] https://en.wikipedia.org/wiki/Dosimetry

    [3] https://en.wikipedia.org/wiki/Ionization_chamber

  2. bunnie says:

    Thanks for the extra info Christian! That’s really interesting.

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