Re: 49 tank sending unit
Posted by HH56 On 2017/5/23 16:18:27
In post 6 I mentioned hooking up a 22-23 gauge and sender to see what was happening with the bimetal type sender. Here is is.
I made notes on the scope photo but basically the gauge and sender heaters are in series and are somehow able to work with each other and know what the two separate pieces are doing. Haven't figured the "how that part works" exactly but I suspect it has to do with the specific resistance of the heaters and maybe the changing characteristics of resistance wire as it heats. The composition and characteristics of the bimetal is probably a factor too.
At any rate when the needle needs to go higher the contact closes to ground so the gauge heater gets a jolt and quickly moves to position. Once it reaches where it needs to go the sender contact starts pulsing to give it just enough heat to maintain position.
When the needle needs to fall the contact stays open longer letting the gauge cool and needle drop. Again, when it reaches the needed position the sender starts a maintaining pulse.
After seeing this action I don't see an ordinary timer circuit being able to duplicated the sender and not sure how accurate the straight resistance type will be. Granted the comparative high resistance of a conventional resistance sender will not provide as much quick heat as the 6v and ground of the bimetal sender. That may be what is enabling the resistance sender to work in maintaining the needle position short term.. The proof will be how accurate it is long term. Am anxious to hear more long term info on how Tinman_70s conversion works out and what value sender he settled on.
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I made notes on the scope photo but basically the gauge and sender heaters are in series and are somehow able to work with each other and know what the two separate pieces are doing. Haven't figured the "how that part works" exactly but I suspect it has to do with the specific resistance of the heaters and maybe the changing characteristics of resistance wire as it heats. The composition and characteristics of the bimetal is probably a factor too.
At any rate when the needle needs to go higher the contact closes to ground so the gauge heater gets a jolt and quickly moves to position. Once it reaches where it needs to go the sender contact starts pulsing to give it just enough heat to maintain position.
When the needle needs to fall the contact stays open longer letting the gauge cool and needle drop. Again, when it reaches the needed position the sender starts a maintaining pulse.
After seeing this action I don't see an ordinary timer circuit being able to duplicated the sender and not sure how accurate the straight resistance type will be. Granted the comparative high resistance of a conventional resistance sender will not provide as much quick heat as the 6v and ground of the bimetal sender. That may be what is enabling the resistance sender to work in maintaining the needle position short term.. The proof will be how accurate it is long term. Am anxious to hear more long term info on how Tinman_70s conversion works out and what value sender he settled on.
Attach file:
(123.17 KB)
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