Re: For sale: 1948-50 Fuel sending unit #403066 NOS

Posted by HH56 On 2021/6/20 16:23:57
Quote:

longjohn wrote:

Ohm readings go from infinite in the empty position to 9-10 ohms in the full position.
I don't think there is anything special about the gasket, I just don't have it.


Unlike the prior years and the 51-6 senders which are of the straight change in resistance type, the 48-50 senders are basically a set of contacts which cycles on and off to ground. A heater in series with the gauge heater and receiving some kind of feedback from the gauge heater controls a bimetal strip in the sender which bends to open or close a contact. I suspect the feedback is via a special wire the gauge heater is wound with that is a type which changes resistance with temperature. The resistance has a carefully calibrated value at known temperatures the gauge heater needs in order to move the needle to a specific place and that changing resistance slows or speeds the sender heater. The other factor controlling the on state and how often it cycles depends on how much force the float or the oil pressure pushing against a diaphragm is adding to the bimetal strip.

Here is an oscilloscope photo showing electrically what is happening.

Attach file:



jpg  22-23 bimetal sender action.jpg (149.83 KB)
209_60cfb0ec2f4f6.jpg 1280X1089 px

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