GPO Indicator Gas No5 - UK Vintage Radio Repair and Restoration Discussion Forum

mole42uk · 15th Apr 2018, 6:20 pm

I recently bought a GPO Indicator Gas No5 in an auction. The instrument is clean and cased but no further information is known. The meter scale reads "Percent Explosive" at the top. I was told it is for sampling the atmosphere in underground spaces before venturing in with tools.

Has anyone any information about these devices?

Dave Moll · 15th Apr 2018, 8:37 pm

If you're a member of the Telecommunications Hertitage Group, there are lots of documents about this on their resources web site.

philthespark · 15th Apr 2018, 10:03 pm

Ah, so you've got an IG5 then! We used them a lot when I was at BT, (http://www.jmwlimited.co.uk/IG5_Indi..._Detector.html)
They are pretty robust,they had to be, the quickest way to kill one was to suck water into it, they have a filter that goes in the sampling line to prevent debris and water being sucked into the sensor, they are a handy tool for checking for flammable gas in chambers and cabinets, although iirc they are designed for natural gas and don't like petrol fumes.
Somewhere I have my original BT training manual and I'm sure it has the operating manual in it, I'll dig it out and copy it for you.

mole42uk · 16th Apr 2018, 7:36 am

Mine seems to be an early one, it has a canvas case but looks otherwise just like the one detailed in the link above.

I bought it because no-one else wanted it at a tools auction, and I liked it because it has "PERCENT EXPLOSIVE" on the meter dial. That attracted the schoolboy in me!

Dave Moll · 16th Apr 2018, 9:18 am

Quote:

Originally Posted by mole42uk

I bought it because no-one else wanted it at a tools auction...

In that case I assume you paid somewhat less than the 198 quid in the linked page!

mole42uk · 16th Apr 2018, 12:14 pm

It was £196 cheaper.....

mole42uk · 16th Apr 2018, 12:22 pm

Quote:

Originally Posted by philthespark

Ah, so you've got an IG5 then!

Somewhere I have my original BT training manual and I'm sure it has the operating manual in it, I'll dig it out and copy it for you.

I'd love to see that if you have time!

Station X · 16th Apr 2018, 1:35 pm

ISTR that these had a piece of metal hanging down, so that it would cause ripples when it hit water. It was then time to stop lowering the probe before it sucked in water.

mole42uk · 16th Apr 2018, 1:41 pm

Mine has that piece of metal. I wondered what it was for.

Dave Moll · 16th Apr 2018, 2:44 pm

Quote:

Originally Posted by mole42uk

It was £196 cheaper.....

Yes, that's the sort of price when I start feeling sorry for a vaguely interesting lot on the basis that I've not lost much even if it proves useless.

qazxsw123 · 16th Apr 2018, 6:36 pm

the sensor is a heated wire, in a bridge cct. the resistance of the wire changes when the gas is passed over it thus altering the bridge and changing the display on the meter. they take a load of U2 1.5v batts. the switch and meter will have a batt test position. the sensor is damaged by the petrol vapour that leaves a coating on the wire. there was a filter unit to be inserted in the sensor line if petrol contamination was expected. and yes when a petrol tank in a garage leaks it finds its way into the cable ducts.

you should be able to test it using the gac cooker, just turn it on for a second and then test the air around it.

15th Apr 2018, 6:20 pm	#1
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,608	GPO Indicator Gas No5 I recently bought a GPO Indicator Gas No5 in an auction. The instrument is clean and cased but no further information is known. The meter scale reads "Percent Explosive" at the top. I was told it is for sampling the atmosphere in underground spaces before venturing in with tools. Has anyone any information about these devices? __________________ Richard Index: recursive loop: see recursive loop

15th Apr 2018, 8:37 pm	#2
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,127	Re: GPO Indicator Gas No5 If you're a member of the Telecommunications Hertitage Group, there are lots of documents about this on their resources web site. __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

15th Apr 2018, 10:03 pm	#3
philthespark Pentode Join Date: Oct 2017 Location: Newton-le-Willows, Merseyside, UK. Posts: 158	Re: GPO Indicator Gas No5 Ah, so you've got an IG5 then! We used them a lot when I was at BT, (http://www.jmwlimited.co.uk/IG5_Indi..._Detector.html) They are pretty robust,they had to be, the quickest way to kill one was to suck water into it, they have a filter that goes in the sampling line to prevent debris and water being sucked into the sensor, they are a handy tool for checking for flammable gas in chambers and cabinets, although iirc they are designed for natural gas and don't like petrol fumes. Somewhere I have my original BT training manual and I'm sure it has the operating manual in it, I'll dig it out and copy it for you.

16th Apr 2018, 7:36 am	#4
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,608	Re: GPO Indicator Gas No5 Mine seems to be an early one, it has a canvas case but looks otherwise just like the one detailed in the link above. I bought it because no-one else wanted it at a tools auction, and I liked it because it has "PERCENT EXPLOSIVE" on the meter dial. That attracted the schoolboy in me! __________________ Richard Index: recursive loop: see recursive loop

16th Apr 2018, 12:14 pm	#6
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,608	Re: GPO Indicator Gas No5 It was £196 cheaper..... __________________ Richard Index: recursive loop: see recursive loop

16th Apr 2018, 1:35 pm	#8
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: GPO Indicator Gas No5 ISTR that these had a piece of metal hanging down, so that it would cause ripples when it hit water. It was then time to stop lowering the probe before it sucked in water. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

16th Apr 2018, 1:41 pm	#9
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,608	Re: GPO Indicator Gas No5 Mine has that piece of metal. I wondered what it was for. __________________ Richard Index: recursive loop: see recursive loop

16th Apr 2018, 6:36 pm	#11
qazxsw123 Triode Join Date: Nov 2016 Location: Frinton on Sea, Essex, UK. Posts: 45	Re: GPO Indicator Gas No5 the sensor is a heated wire, in a bridge cct. the resistance of the wire changes when the gas is passed over it thus altering the bridge and changing the display on the meter. they take a load of U2 1.5v batts. the switch and meter will have a batt test position. the sensor is damaged by the petrol vapour that leaves a coating on the wire. there was a filter unit to be inserted in the sensor line if petrol contamination was expected. and yes when a petrol tank in a garage leaks it finds its way into the cable ducts. you should be able to test it using the gac cooker, just turn it on for a second and then test the air around it.