What component is this? "Sensitive relay" with uA meter - Page 1
Forum section: electronics / general

author: mvno_subscriber
author_rank: Regular Contributor
timestamp: June 10, 2025, 06:21:23 pm
content: Found this in an old bin in an old shop. At first I thought it was a normal panel meter, but then I saw all the connections. Is this a relay? And how does it operate? Anyone knows?

author: SteveThackery
author_rank: Super Contributor
timestamp: June 10, 2025, 07:25:53 pm
content: I suspect it closes an electrical contact when the needle reaches either extreme of travel. The stops at either side look unusual - not just the normal pins you see on other meters.

author: Gyro
author_rank: Super Contributor
timestamp: June 10, 2025, 07:41:02 pm
content: It's also known as a moving coil relay, albeit one with a nice meter scale. The knob to the right of the center adjusting screw should set the contact position, and hence the sensitivity.The contacts have a very low rating, in the past they would have fed a larger relay coil (with appropriate snubber network). These days you can just use them to drive a switching transistor.The applications are mostly historical, replaced by semiconductors, but it's an interesting item with direct readout.

author: NE666
author_rank: Frequent Contributor
timestamp: June 10, 2025, 07:46:48 pm
content: Seems to be a variant of their "Sensitrol" relay.

author: SteveThackery
author_rank: Super Contributor
timestamp: June 10, 2025, 08:38:02 pm
content: Wonderful!

author: TimFox
author_rank: Super Contributor
timestamp: June 10, 2025, 08:47:13 pm
content: In the movie "Apollo 13", while one team is working with all the items available to the stranded astronauts (including manual covers and duct tape) to specify how to adapt filters to ductwork, another engineer is carefully checking out the sequence of switch flips to avoid tripping the circuit breaker. He is using a similar Simpson "meter relay", configured as test equipment rather than panel meter.This is my memory of the meter, but I can't locate the model online. Simpson, Triplett, and Hoyt all made them as panel meters, here is a modern catalog listing with explanation of function:https://lfemeters.com/pdf/lfe_api_12.pdf(Note: that first movie scene is a bit fictional, apparently they were working from a detailed inventory list rather than a pile of junk on the table.)

author: SteveThackery
author_rank: Super Contributor
timestamp: June 11, 2025, 04:33:09 pm
content: Quote from: TimFox on June 10, 2025, 08:47:13 pmReally? If I were involved, I absolutely would convert that inventory into a "pile of junk on the table". Think how difficult it would be without the physical objects to examine. How many people would be able to remember every dimension of an item just by looking at its entry in the inventory? How difficult would it be to assemble a bunch of parts in your mind's eye, knowing only what tbey look like in the paperwork?Of course I wasn't there so I will never know, but surely they must have had the parts in front of them to play with.And what a truly magnificent achievement it was: NASA and the people involved did something extraordinary. As it suggests in the film, the rescue of Apollo 13 might be NASA's (and perhaps America's) finest achievement.

author: TimFox
author_rank: Super Contributor
timestamp: June 11, 2025, 09:54:18 pm
content: The pile of junk on the table made for better cinema, certainly.

author: coppercone2
author_rank: Super Contributor
timestamp: June 14, 2025, 07:42:38 am
content: I think they must have had it, the hallmark of a bad work place is the one that does not want to spend small amounts of money on physical prototypes and expects insane mental gymnastics from engineers. Unless its a massive volume or price problem its just IMO bad engineering practice. I noticed the people that don't get samples and stuff hardly ever get anything done... and no one approves their projects because it eventually goes to someone that thinks WTF is this, let me see it on the table. I knew one guy that was doing that and I think it was just a defense strategy to keep me out of his simple work, obviously I ditched that shit. It starts with someone arguing not to cut a piece of twine to figure out the wire length through some convoluted jumble of crap for instance, or god forbid you cut a wire too long, from the 500 foot spool of PVC with the 1967 date code on it... I guess you win a medal for spending all day trying to figure it out without actually doing it...