Thursday, May 26, 2011

2011-05-26 21h CEST - Measurement briefly interrupted by a malfunction in the FH40T

Goes, 2011-05-26 22:19 CEST:
Tonight around 21h, the readings from the FH40T suddenly ceased. No more clicks were detected. After some initial testing, no immediate cause for this malfunction could be found, the FH40T detection electronics seemed dead but fortunately the G.M. tube was still OK.

After an interruption of about an hour, I was able to continue the measurements with a spare (D.I.Y) counter circuit that I had already built, using the same G.M. tube FHZ76V.

I''ll try to repair the FH40T in the near future, or otherwise I'll try to build new electronic circuit and integrate an LC-Display into the FH40T housing. Something which I already had planned to do, but hesitated to destroy a functional Radiation detector.
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4 comments:

  1. Fred in TokyoMay 27, 2011 at 10:28 AM

    One of my 2 FH40T also died a few weeks ago.
    The GM tube also still ok.
    Maybe the HV transformer or bad caps?
    yes lets take it apart now!
    In both my FH40T there was and is a an annoying 2400Hz tone from the HV circuit which might be due to bad Caps.
    There is rubbish inside the analog galvano meter as well which prevents it from moving sometimes. Good idea to replace with LC-display and your counting circuitry.
    The audio-connector better be replaced as well it is a source of unwanted cracks sometimes(and trigger events) now in the audio-signal (gold-plated mini audio-jack?).

    cheers,
    Fred

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  2. katzeMay 28, 2011 at 2:20 PM

    Normally, military equipment like the FH40T are made to last almost forever. If the HV circuit is still ok it would be not a big deal to repair the detection part. Normally the pulses are decoupled with a small capacitor and can easily be brought to a 5V level with a zener diode and then be fed into the microcontroller.

    Watching the "new" values, they are slightly higher then before. Maybe you are more to the right of the plateau now, with a higher voltage level.

    I suggest to put the radiation graphs on the intro part of your page. visitors would be happy to see them immediatly.

    Did you recieve my email concerning the SI8B tube datasheet?

    Greetings,
    katze

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  3. radiation-goesMay 28, 2011 at 9:05 PM

    To Fred: Thanks for your feedback.
    I've measured the HV (with a 100MegOhm load of a Multimeter with "high impedace" (the well-known 90Meg series resistance):
    HV is still present but way too low (240Volt) (far under the starting voltage of the tube).
    The annonying 2400Hz is also audible but much weaker than it was before. So I suspect some component in the HV circuit has gone bad, probably a Cap.

    I'm doubting whether to try and repair or to dump the circuit (find the circuit diagram first) and build it all new (and digital).

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  4. radiation-goesMay 28, 2011 at 9:26 PM

    To Katze: thanks for your feedback. It seems that the HV is at fault (see my other response).

    About the "new values": The tube is not in the (external probe) but completely in the open, and it mounted close to a (slightly opened) window.

    Thanks for the email about the SI8B, your info was very welcome :-)

    regards, RadGoes

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