# Measure position with magnetic resistive sensor

Hello,
a friend of mine owns a milling business and several years ago, he bought a computer-steered milling machine that he eventually wants to fire up. He being in Belgium found a company in Italy that would like to help him out replacing the existing old computer and replace it by a new PLC.
He spoke to me about some sensors on that machine to measure the actual position on the blade. The Italian company’s advice is to replace these as they cannot be read by their PLC. Problem is that there are 5 of those and they each cost about 2000\$. So I proposed that I would see what the Arduino can do in this case to keep the existing sensors.

For starters, I don’t know exactly what kind of sensor this is. Here is a picture: Sensor complete.
It is a metal rod that is connected (picture) with an 8-wire cable(picture). The rod runs through a part that defines the position (picture). In fact this rod, when in the machine, runs through 3 of those position parts.

While googling for some information I thought it might be some kind of magneto resistive sensor, but I’m not sure because the position part is not magnetic at all. I also bumped to this explanation of how to use that kind of sensors with Arduino. I learned that it is about measuring the resistance in the sensor.

So before experimenting myself with this sensor I hoped for someone to help me out on this. Therefor, I started with measuring the resistance between the 8 wires of the sensor. I measured the resistance WITHOUT the position part on the rod. I’m not an electronic specialist, so I just put my multimeter on 2000 and start measuring. When the value remained 1 (meaning infinite resistance, indicated as +), I increased the scale to 20k, 200k, 2000k. I also noticed that when there is a measurable resistance over 2 wires, changing the polarity of the multimeter returned 1. Therefore, I will post the results as a matrix where the COM was always on the columns (and this the red one on the rows):

| | Blue
| Brown
| Red
| White
| Pink
| Grey
| Green
| Yellow
| | | MM scale | | | COM |
| - | - | - | - | - | - | - | - | - | - | - | - | - |
| Blue
| -
| +
| 560
| +
| 580
| 580
| 1265
| 1265
| | | 2000 |
| Brown
| +
| -
| +
| 152
| +
| +
| +
| +
| | | 2000 |
| Red
| +
| +
| -
| +
| 7,400
| 7,400
| 15,70
| 15,70
| | | 20k |
| White
| +
| 151
| +
| -
| +
| +
| +
| +
| | | 2000 |
| Pink
| +
| +
| 629
| +
| -
| 2
| 434
| 434
| | | 2000 |
| Grey
| +
| +
| 619
| +
| 2
| -
| 433
| 433
| | | 2000 |
| Green
| +
| +
| 59,4
| +
| 50,5
| 50,6
| -
| 109,8
| | | 200k |
| Yellow
| +
| +
| 59,2
| +
| 50,4
| 50,2
| 108,6
| -
| | | 2000 |

So, does this makes sense? Should I measure this in another way? What is the next step to do?
All help is REALLY appreciated as this can save my friend a lot of money when it is possible to read the sensor with an Arduino.

Thanks!
David

Are the sensors totally unmarked?

Sorry for the pictures. Now I have put them in a shared album and used those links. Can you please try again?
And indeed, all the parts are unmarked, so I guess it is custom made ...

Thanks!
David

It seems very likely that some sort of electronic circuitry is inside the device, and with 8 wires, it is just about hopeless to reverse engineer without taking one apart completely. Resistance measurements won't tell you much.

If you know the cost of the sensor, why don't you have any more information about it?

I don't know the cost of this sensor because the Italian company proposes to replace them by other sensors so that their PLC can read them. That is the reason why I posted this ...

Unless you can get the information from the original manufacturer of the milling machine, in my opinion, those sensors are not worth the effort to revive.