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| L-1011 Engine Oil Pressure - Smiths' Ltd. |
The Engine Oil Pressure indicators used on the Lockheed L-1011 are made by Smiths. All in all there are three of these, one for each engine. They have a range from 0 to 100 psi in increments of 5 psi. Pressure range markings are red from 0 to 35 psi, yellow from 35 to 40 psi and green from 40 to 100 psi.
The three indicators have a common test switch on the panel (not shown in this posting). The test switch will drive the indicators to about 22 psi.
To indicate pressure the instrument would send a 400Hz SIN and COSIN signal to a sensor. The oil pressure presses down on a piston that then moves a coil that sends back a phase shifted signal to the instrument. The phase difference between the 400Hz reference signal and the signal produced by the sensor is then indicated as the pressure on the front of the instrument.
The image below shows a simulated phase shifted signal that outputs the 55 psi you see in the image at the top of this posting. The phase shift can be somewhat reproduced with a digital potentiometer, however, a much more elegant way would be with a resolver or a Digtial to Synchro Converter. The video at the bottom of the posting shows the instrument in action receiving a number of different wave offsets.
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| L-1011 Engine Oil Pressure Indicator - Phase Offset |
Here is the schematic and pinout for the L-1011 Engine Pressure Indicator made by Smith Ltd.:
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