Hall sensor as limit switch

Thread Starter

k9electroman

Joined Nov 2, 2011
2
I am driving a axis with a stepper motor and want an accurate home switch. The problem is my work environment is 77 Kelvin. The hall sensor i am using the FH-301-040 by FW BELL. This is because it works in extreme cold and cheap ones don’t. The motor controller needs digital input (>2.2volts) to sense "home" but the hall sensor only outputs 30ma. :confused:

What kind of control circuit can I use?

Here are the specifications of the hall sensor.
fwbell.com/file/FH-300_500.pdf

 

praondevou

Joined Jul 9, 2011
2,942
That's one of the worst datasheets I've seen. Even on their website I didn't see much more information about it.

The only thing that is quite explicit is that the output is a voltage output.

"With field direction (+B) as shown <obs. shown where?> and Ic entering the Ic (+) terminal, the positive Hall voltage will appear at the VH(+) terminal"

Are you sure you mean 77 KELVIN ??? This sensor works down to -55 Celsius, that's 218K so it would not work anyway.
 

Thread Starter

k9electroman

Joined Nov 2, 2011
2
I agree the spec sheet is lacking. Yes I am sure about the temperature "77.36K". That is liquid nitrogen’s boiling temp. Most component specifications only go to -55F (224.8K) so I must do my own testing down to 4K. Some things work, most don't. I hear this hall sensor works cold, down to 30K. I just can’t figure out how to drive it accurately.
 

praondevou

Joined Jul 9, 2011
2,942
I just can’t figure out how to drive it accurately.
Me neither. It's not described in the datasheet. You could try to pass the nominal current through the Ic terminals and see what happens to the output voltage when applying a magnetic field.
I would contact the manufacturer directly. Also, according to the datasheet it works only down to -55 Celsius.
 

John P

Joined Oct 14, 2008
1,785
Could you replace the magnetic switch with an optical one, with the transmitted and received light beams traveling down optical fibers? That way the electronics could stay in a warm environment. I doubt if there are any components specified for temperatures below 100K.

Edited to say: If the electrical properties continue to work at very cold temperatures, could you use an inductive or capacitive sensor? I can imagine ways to do either of those.
 
Last edited:

bertus

Joined Apr 5, 2008
20,236
Hello,

In our company we are using electronics on very low temperatues to reduce the noise:

CryoProbe Mechanics


CryoProbe technology takes advantage of the fact that the radio frequency electronics will generate a higher signal and less noise at lower temperatures. By reducing the temperature of the NMR coil and preamplifier signal to noise ratio, enhancements of a factor of four or more can be achieved. This can easily translate into an order of magnitude higher throughput. The coil assembly and preamplifier are cooled using cold helium gas in a closed-loop cooling system. The closed-loop cooling system, in which helium gas is compressed in one chamber and then allowed to expand in a second chamber, produces the cold helium gas. Vacuum-insulated parts in the cooling system allow the coil assembly to reach very low temperatures. Thermal isolation in the probe is critical to allow samples to be measured at room temperature only a few millimeters from the cold coil assembly.
So it is possible to use special electronics at very low temperatures.

Bertus
 
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