Reply To: electronic cylinder indication

[Werner SchleidtParticipant @wernerschleidt45161]

Part 2

The displacement sensor or the piston travel sensor is more tricky. I want to have a sensor who is on small and bigger engines possible to install. I had an incremental angle sensor this is very accurate but it have to be attached to the axle or flywheel and that is not so easy without changes at the model or object. I get by chance a very fine LVDT displacement sensors with a carrier amplifier and inbuilt electronic. To meassure 100 mm the sensor is about 300 mm long. This is difficult to mount. So i came to the results that the sensor mechanism with a rope like in the old indicators is very favourable. So i thought about about how i can build a sensor. In my former job i know rope displacement sensors based on a rope a return spring mechanism and a rope drum and a potentiometer. This parts are very expensiv , the range is from 500 to 1000 €

So i construct my own. The base is a multiturn wire potentiometer with 5 Kohm , a drum which is coupled with the potentiometer axis and a return spring i got from a identicard jo jo. This were my parts which play together to operate the rope sensor. My modelplane colleague Herbert sponsored me with thin multiwire control line rope.

It was very tricky to bring all parts together and after the first one i made two others all in a range of max 300 mm. I tested them in comparison to my digital gauge at the milling machine. The measurements were very repeatable and with a good accuracy. I added a small amplifier with a filter for cutting noise and with a level shifter for easy zero shift adjustment. The span was precalibrated at the amplifier and a fine calibration can be made by software. All sensors have a unique calibration file, but the rope sensor are very similar.

To give you an idea from my sensor

The spring is in the frontside of the drum . In the front cover of the housing there is a screw which is the spanner for the spring. The tricky part is adding the rope winding by winding in the right direction and spanning the clock spring and setting the potentiometer at the correct position. This is a four hand job, but with several try's it worked good. The amplifier ist then attached to the potentiometer and then it was added some heatshrink tube. Then the parameter and calibration was measured and marked at the sensor.

In the next picture it is adapted to my loco for measurement.

The pressure sensor is connected to the cylinder cover. The rope sensor is mounted with some improvisation with clamps and wooden bars at the front. The rope is connected to the crosshead by a chain and a adapting screw. The white PA part allows clamping of the sensor and some adjustment.

part 3

Werner

 

 

 

Edited By Werner Schleidt on 15/09/2021 18:03:05