There are a lot of after market water temp; transmitters about.
This is what an original one should look like.
When cleaned off the body should be in copper, not brass and etched on the casing are the words
" Smiths Industries LTD. Made in U.K. " .
The resistance should be about 900 ohms at room temperature.
Tony.
Edit July 2018 : These temperature senders have a problem after use for some years. The earthing for the gauge / sender is from the copper sensor casing to the mild steel of the threaded section. Over time this connection deteriorates and the gauge reading drops from normal. The solution is to use silver loaded epoxy on the join between the copper and the steel after cleaning it up. In my case the earthing resistance was around 300 ohms. Cleaning and adding the silver epoxy reduced this to <1 ohm.
And some measurements.
1. A set of data points relating water temp; gauge reading to the simulated temperature sender resistance with constant 13.5V in to the mechanical voltage stabiliser ( nominal 10V output) with a simulated load of 150 ohms for the fuel gauge.
First indication : 180 ohms.
"1/4" on the gauge : 100 ohms.
"1/2" = N on the gauge : 68 ohms.
"3/4 on the gauge : 47 ohms.
Full scale : 22 ohms.
So, very non-linear
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orig temp tx.JPG [ 64.35 KiB | Viewed 2418 times ] |