Ludlum 12 Ratemeter Issues

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
Jackson Oswalt
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Ludlum 12 Ratemeter Issues

Post by Jackson Oswalt » Wed Jan 03, 2018 3:02 am

Once again, eBay has gifted me another expensive item that doesn't quite work. I just can't catch a break, but hopefully this item will end up being the exception. Recently, I purchased a BF3 detector tube along with the a Ludlum 12 ratemeter. According to the seller, the ratemeter is "in good condition" and he/she never mentioned if it had been tested or not. I assumed good condition meant working, but maybe that was my mistake. Anyways, the problem is it completely fails the battery test. The meter barely moves.Interestingly, if I get it more than 1.5v (it takes two D batteries), the meter makes it farther. However, even at 10 volts it's only half way there. Does anyone have any idea why this could be? My biggest regret is that a messed a few potentiometers, but none that would normally be under the "calibrate tab" (which this model doesn't have).
image.jpeg
Ludlum 12 Ratemeter
Interestingly, the one screw on the face plate of the gauge isn't holding the face plate on. It seems to be a potentiometer, as it makes the needle jump up and down (although never close to where it should be). Hopefully someone will have an answer to this.

Thanks!

-JO
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ian_krase
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Re: Ludlum 12 Ratemeter Issues

Post by ian_krase » Wed Jan 03, 2018 5:36 am

It's normal for the one "screw" in the front of a panel meter to be a zero adjust.

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Frank Sanns
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Re: Ludlum 12 Ratemeter Issues

Post by Frank Sanns » Wed Jan 03, 2018 5:47 am

You have two equations and two unknowns. Unfortunately, until you can quantify one of them, you will have a devil of a time trying to get them both working together. As you are attempting, get the meter working first.

The black screw on the black faceplate is to adjust the mechanical zero on the meter. The screw mechanically moves the meter movement and is not a calibration. It simply sets the movement zero.

Assuming you have two good batteries, I would assume ignore the meter reading for the moment. Check the HV with a volt meter and see if it adjusts with the HV potentiometer below the RED reset button. If that is working, set it to around 800 volts and connect a Geiger tube. Then adjust the gain to get counts with a radiation source present.

If this checks out then your meter is working and you can do a calibration at this point. Once that is done, attach you BF3 tube and run the voltage up until you start to get counts. This will most likely be in the 1,500 to 2,000 volt range. You may have to adjust the gain as the signal on the BF3 and the Geiger tube once you get to that point.

You can find the procedure to set the gain in the Radiation FAQ area.

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Dennis P Brown
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Re: Ludlum 12 Ratemeter Issues

Post by Dennis P Brown » Wed Jan 03, 2018 12:06 pm

Two very possible problems: first, (and hopefully, the least likely) if the battery contacts are bad or not making proper contact, it is very easy to measure low battery on the meter display (assuming your batteries are new - 1.6 volts each.) Assuming the batteries are fresh and put in correctly, press down on the battery cover as you test the batteries - if it jumps up in volt, the contacts are the issue.


Next (and hopefully this isn't an issue due to not reading the manual), these batteries MUST go in in a very specific manner/order! They need to create 3.0+ volts - that is, they are in series, not parallel. I do not have your meter so look up the manual and get the correct order arrangement (proper pos/neg order) - that matters a great deal (i.e. the unit will not work.)

Aside: it sounds as if you might not have read the operation manual - if not, do so. It is very useful.

Jackson Oswalt
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Re: Ludlum 12 Ratemeter Issues

Post by Jackson Oswalt » Thu Jan 04, 2018 1:16 am

I have read the manual and the batteries are in the correct position, but the meter outputs no power still. I've been messing with it the entire evening with no results.
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Bruce Meagher
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Re: Ludlum 12 Ratemeter Issues

Post by Bruce Meagher » Thu Jan 04, 2018 3:23 am

I’ve had many problems with Ludlum's battery compartment causing faulty or flakey power to the electronics on their old meters. When in doubt check the power at the the board with a DMM. The most common problems I’ve seen are oxidized terminals (top and bottom) and faulty springs. It might not be that simple in your case, but something you should double check. The schematics are in the manual (although you might have to search for the matching revision). Try tracing the battery signal to the meter and report your findings.

Jackson Oswalt
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Re: Ludlum 12 Ratemeter Issues

Post by Jackson Oswalt » Thu Jan 04, 2018 3:26 am

After fiddling with it even more, I managed to get the meter to output by taking the batteries out of the case and applying them via the terminals on the inside of the meter. This means there must be something wrong with the contacts.
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Dennis P Brown
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Re: Ludlum 12 Ratemeter Issues

Post by Dennis P Brown » Thu Jan 04, 2018 12:37 pm

One of my battery wires had a an issue within the wire - must have been broken making poor contact. I replaced it and that fixed one of my battery issues. The other is an internal spring which, due to corrosion, I can't replace. So, I installed an external battery (not saying do this later part.) So, do also Ohm the wires that lead from the batteries.

Also, minor corrosion on the selector switch assembly (the massive one with the many wires) did create some issues. Used a tuner cleaner and lube spray and improved performance.

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Richard Hull
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Re: Ludlum 12 Ratemeter Issues

Post by Richard Hull » Thu Jan 04, 2018 4:22 pm

The biggest idiocy in all of nuclear counterdom is.......

Installing fresh alkaline batteries in a GM counter and leaving those alkaline batteries in the unit for more than 1 week.

The secret is to place any and all batteries in the counter only at every use and remove them immediately after the present pressing need and use of the counter goes away.

In this manner, and only in this manner, will all contacts remain flawlessly operational for at least as long as you own the counter.
Some folks seem to think that leaving batteries in a counter for a period of non-use for 6 months, 1 year, a decade,etc., means they can expect to use it at any time during that period.

Alkaline batteries are among the worst leaking offenders and have destroyed and damaged more contacts and even internal electronics than any other form of battery chemistry. In the same breath, no battery is better suited for a month long trip into the desert for uranium hunting than alkaline batteries. The secret is to remove them immediately upon arriving home. The best GM counter to have and use at home is a wall powered counter. It is all to easy to set a portable counter aside with batteries in it, at the ready, and forget them just long enough to destroy the contacts or leak all throughout the meter. The chemicals contained in alkaline batteries are extremely aggressive.

A Ludlum is a prize instrument and it is all too easy to remove and re-install batteries in them than to use them as a test chamber for rotting batteries.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Jackson Oswalt
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Re: Ludlum 12 Ratemeter Issues

Post by Jackson Oswalt » Thu Jan 11, 2018 1:17 pm

After attempting to connect my bf3 tube, the meter stopped outputting power. Just all of a sudden. It didn’t make a noise or anything. Does anybody know why this is and how I can fix it? Thanks.
The Youngest Fusioneer At 12 Years Old

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