Well...To revive a year old thread...
I ordered and installed on of these Magneto resistive units:
http://www.sybasystems.com/FM%202%20sender/fm%202%20sender.html
I ordered a 0 ohm to 10k ohm sensor assembly after testing with a 10k pot on an input on the M1 control board. As mentioned in several other threads and in this one, the voltage readings are not linear with this type of set up on the M1. I decided after testing on the M1 with the 10k pot that I would get the resolution I needed. All I am really concerned with is Empty and maybe quarter tank measurements at the most. Right now I am using the Elk as an analog zone only. I am using an ISY994 from Universal Devices to query the zone voltage every minute. It sends an email when I hit below 0.3 volts for empty, and above 10 volts for a tank filled message. There are is also some variables involved to make sure if there is a bit of switching between marginal measurements to make sure I don't get any more than one email. I still have some research to do when the tank is filled but I'm sure that will be pretty soon with the current temps in PA.
Overall the ordering experience was good. I called and provided the details of what I was looking to do. They asked a few good questions like the maximum current that will be flowing, and after some measuring and discussion, the quarter watt resistors in the sensor will be plenty. I gave them a credit card over the phone and that was it. A few days later the probe arrived. It was packaged well in a long box with some 1x3 looking boards along two of the 4 sides of the box to protect it from damage.
I took some actual resistance and voltage measurements with the sensor out of the tank while hooked up to the Elk Zone. The resistance was taken first unhooked and then the voltage was taken hooked up, (obviously). You'll see that the voltage climbs quickly in the first half of the stick. I got 38 different points of measurement. Maybe this unit didn't have the 56 that I remember talking about but I really wasn't that concerned. Once again a minor detail for the resolution that I needed.
Here they are:
1.5 ohms. 0.011 volts
218 ohms. 1.378 volts
455 ohms. 2.590 volts
693 ohms. 3.589 volts
990 ohms. 4.615 volts
1288 ohms. 5.455 volts
1587 ohms. 6.154 volts
1885 ohms. 6.75 volts
2180 ohms. 7.25 volts
2480 ohms. 7.70 volts
2778 ohms. 8.08 volts
3074 ohms. 8.42 volts
3311 ohms. 8.66 volts
3548 ohms. 8.89 volts
3784 ohms. 9.08 volts
4020 ohms. 9.27 volts
4258 ohms. 9.44 volts
4495 ohms. 9.60 volts
4733 ohms. 9.75 volts----half stick
4950 ohms. 9.88 volts
5168 ohms. 10.00 volts
5405 ohms. 10.12 volts
5642 ohms. 10.24 volts
5939 ohms. 10.37 volts
6236 ohms. 10.49 volts
6533 ohms. 10.61 volts
6840 ohms. 10.72 volts
7140 ohms. 10.82 volts
7440 ohms. 10.92 volts
7730 ohms. 11.00 volts
8040 ohms. 11.09 volts
8270 ohms. 11.15 volts
8510 ohms. 11.21 volts
8750 ohms. 11.27 volts
8990 ohms. 11.32 volts
9220 ohms. 11.38 volts
9460 ohms. 11.43 volts
10250 ohms. 11.58 volts
Elk Open circuit 13.81 volts
There is only one thing that I noticed that I didn't think would be an issue. The 0 ohm range is about the bottom 2 inches of the stick. From there on up the distance between readings was a very close 1" or so.
Also, in the picture of the unit on the web page, the wire comes out of the side of the assembly. On the unit I received, the wire comes out of the top center of the unit.
