[T2] Gas gage weirdness

[Bob Reuter]

this is correct this wierd little gizzmo is on the back of the guage and 
is vital component

Bob


On Fri, 22 Feb 2019, Robert Mann wrote:

>   A couple y ago we had a vague inconclusive discussion of another part
> shown in your Bentley schematic connected to the fuel guage,* viz*. the
> 'vibrator'.  I gained no understanding of this device, except that its
> function has to do with damping unwanted oscillations on the guage.  For
> all I know, if this enigmatic component goes wrong, the results may be
> those which you've been observing.
>
> Robt Mann
> '73 1600dp Devon camper
>
>
>
> On Fri, Feb 22, 2019 at 1:44 PM c.dreike <c.dreike at verizon.net> wrote:
>
>> Started testing my gas gage and sender. The sender worked when I
>> installed it. Currently the tank is very low and the sender reads about
>> 80 ohms. According to The Samba this is about correct. The senders run
>> from about 3-5 ohms at full to about 70-80 ohms at empty.
>>
>> When connected, both of the gauges I have read full and a little past.
>> The battery voltage is about 11.98. The voltage across the gauges are
>> 6.57 on the original gauge and 7.98 on the reproduction gauge.
>>
>> On the test bench connected to a bench supply, the original gauge reads
>> full at about 6.5V and the reproduction gauge reads full at about 7.2V.
>> As I reduce the voltage to the gauge, the reading goes down. At 0 volts
>> the gauges read empty.
>>
>> Per the test specs in Bentley, the gauges should read full at about 12V,
>> battery voltage. Both my gauges peg when attached to full battery voltage.
>>
>> I have double checked the wiring against the schematics and all looks
>> correct. The circuit looks simple enough. +12V on one side of the gauge.
>> The other side of the gauge connects to the sender (5-80 ohms) and the
>> other side of the sender connects to ground.
>>
>> I'm an electrical engineer with lots of experience with simple stuff
>> like this and this stuff makes no sense to me. I must be missing
>> something. (Kinda like mistaking the wire stripe colors on the turn signal)
>> Anyone have ideas on what I should be looking for or doing differently?
>> I'm stumped. I'm about to build an inverting operational amplifier
>> circuit that would drive the gauge so that it would see 0 volts at empty
>> and about 7V at full.
>>
>> TIA
>> Chris
>> 71 Sunroof
>> 64DD Kamper Kit
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