Re: Need Help Modifying the Low Range Probe from AN/PDR-63
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The '63 is an interesting unit electronically speaking. The low range unit uses a 700V G-M tube, but on some ranges is operated below its Geiger region at 550 or 570V. Naturally it doesn't count at the HV. Why do this? Because all G-M tubes are subject to "saturation" at high count rates.
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What this term means is the tube is literally saturated with radiation coming in so fast, it loses the ability to reset itself between pulses, resulting in a ZERO reading,/ not good.
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In practice this is observed when a user is walking or driving into a radiation field with a G-M instrument, the readings will increase steadily then suddenly drop to zero! High end civilian meters have an alarm, the CDV-700 does not.? In the instructions, the manuals always state that they are for training and in-shelter (low radiation fields) testing of food and water supplies. We're all hobbyists here on this group (for now anyway).
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Military recognized this, that's why there's an ion-chamber unit in the '63 too, to cover those high radiation fields. Some other? RADIACS, instead of an ion-chamber have a very small high-range GM tube piggy-backed onto the main probe body to handle the issue.
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But in the '63 while the low range tube is connected, the higher ranges, way outside it's normal capability are access by reducing the DC? voltage below the threshold of detection, then briefly pulsing an additional Voltage over the top of it to take a single measurement, knowing the tube may saturate, the pulse is very brief and turns itself off quickly, giving the G-M tube time to reset itself for the next pulse. In this way the G-M tube's upper limit of detection is greatly increased. But this is at a cost, since only a fraction of the radiation strikes are actually being reported.
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Some civilian detection units operate with a similar system continuously, therefore their CPM are different from other units using the same tube.
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Keep these facts in mind when seeing something being reported strictly in CPM.
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Also ALWAYS, always, suspect ANY reports given in mR/Hr units form any instrument, unless all the other measuring parameters are listed as well. Many factors are responsible for correct mR/Hr readings.
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Geo
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? From: "STEPHEN CARLILE via groups.io" <smcarlile@...>
To: "CDV700CLUB" <[email protected]> Cc: "tanner carlile" <tanner.carlile@...> Sent: Wednesday, April 20, 2022 6:14:56 AM Subject: Re: [CDV700CLUB] Need Help Modifying the Low Range Probe from AN/PDR-63 ?
Excellent! Thanks,
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