FAG Contamat FHT111M Radioactive Contamination Meter - Page 1
Forum section: electronics / repair

author: dexters_lab
author_rank: Unknown
timestamp: August 25, 2018, 03:15:06 pm
content: Picked up this nice radiation meter the other day, it does have a small issue so posted it here in the repair section...it's a 1995 vintage meter with a large rectangular windowed detector, it can detect alpha, beta and gamma. it can also discriminate out beta/gamma and only measure alpha which is particularly nice. It's Z80 microprocessor based and can accept several types of detector, in this case it's a 166x100mm butane filled gas proportional detector which clips onto the base of the unit where several pogo pins make contact with the anode and a small pad of connections, probably to tell the unit which detector it is.functionally it seems to be working just fine, i've tested it with several of my own sources and background gives around 7 CPSIt's only issue seems to be the gas reservoir as it seems to lose it's gas after about an hour. On the top of the detector there is a refill port which looks like a usual lighter refill port, there is a screw which gives access to the reservoir and then further over there is a outlet vent. On the base there is a purge button.It appears as though a user would fill the reservoir with butane, then depress the purge button to release butane into the detector. The outlet port then vents out excess butane and holds the detector at a defined pressure. The reservoir is supposed hold enough butane for about 5 days of use but mine only seems to retain the gas for about an hour or so.I've changed the easy to get to o-rings on the refill and the reservoir plug screw but it made little difference. I am wondering if the purge button is leaking the butane into the detector all the time which in turn is just vented out.any thoughts on making it more gas tight?

author: eliocor
author_rank: Unknown
timestamp: August 25, 2018, 09:32:17 pm
content: Maybe an hole in the rad-film (metalized mylar): it is very thin and can be easily ruptured.Here you can find some documentation regarding this device:https://www.radioactivityforum.it/forum/viewtopic.php?f=95&t=787I think you need to register to download the documents: I can assure you will never receive any spam from this forum!

author: dexters_lab
author_rank: Unknown
timestamp: August 26, 2018, 09:34:45 am
content: Quote from: eliocor on August 25, 2018, 09:32:17 pmthanks, the foil window seems to be intact and holds pressure so i am sure it's either the purge button or the reservoir leaking.i know the foil windows are (were) replaceable but it seems it's very well stuck onto the body of the tube, removing it will probably damage it too far to use it again so i am reluctant to go furtherthanks for the links to the forum, i'll give them a try

author: Gyro
author_rank: Super Contributor
timestamp: August 26, 2018, 10:27:37 am
content: A couple of thoughs:1. A sniff test, if it's leaking at that sort of rate then you might be able to narrow down the leak with your nose.2. Try immersing it (the head that is!) in distilled water and looking for bubbles? Maybe a bit risky but it ought to dry out ok if there are no contaminants in the water.

author: dexters_lab
author_rank: Unknown
timestamp: September 03, 2018, 09:16:45 am
content: well it seems after some use the meter has largely stopped leaking it's gas with the main reservoir holding some pressure for at least 24 hours now... looks like it just needed to be used a bit.unless i can find a way to ensure i could replace the mylar film on the front of the detector, which would need to be removed before i looked at the gas reservoir i am not going to attempt any kind of repair

author: Mijer34
author_rank: Newbie
timestamp: January 06, 2024, 02:03:49 am
content: I know i reviving this topic, but i need some technical suport with this same meter. I need to conect to my PC and change the threshold because it's annoying. How i can conect this din conector to usb and where i can get the program for operating this meter? I have only german instruction. What i understand from it, there's no operating board or anything like this so just connecting right pins i should easy connect to my PC but i need to be sure. Tahnks for all help.