Circuit to make large voltage drop with small resistance change?
Circuit to make large voltage drop with small resistance change?
(OP)
Hi,
I am trying to make a liquid metal level sensor for our lab. There as the liquid metal is 700C most liquid metal sensors will not work. Due to the nature of the installation remote level sensors such as laser, ultrasound etc are not suitable either.
I would like to use some high resistance wire to make t probes which go into the molten metal, supply a voltage (5 or 10Vdc) and measure the voltage drop across the probes. As the liquid metal is highly conductive it should read 0 when the vessel is empty and contact is not made, and ~5V when the vessel is full and the virtually the entire probe is submerged. I can easily calibrate the sensor.
My problem is that the only suitable resistance wire only has a voltage drop of 6 ohms /foot. The length of the probes is ~1 foot.
If the voltage drop was in K ohms there would be no problem.
My question is, does any one know of how to find resistance wire capable of withstanding 700C with a significant resistance per foot, or is there a way of making an electrical circuit to enable me to effectively drop ~5V across a sensor which is only 6 ohms in resistance?
I am trying to make a liquid metal level sensor for our lab. There as the liquid metal is 700C most liquid metal sensors will not work. Due to the nature of the installation remote level sensors such as laser, ultrasound etc are not suitable either.
I would like to use some high resistance wire to make t probes which go into the molten metal, supply a voltage (5 or 10Vdc) and measure the voltage drop across the probes. As the liquid metal is highly conductive it should read 0 when the vessel is empty and contact is not made, and ~5V when the vessel is full and the virtually the entire probe is submerged. I can easily calibrate the sensor.
My problem is that the only suitable resistance wire only has a voltage drop of 6 ohms /foot. The length of the probes is ~1 foot.
If the voltage drop was in K ohms there would be no problem.
My question is, does any one know of how to find resistance wire capable of withstanding 700C with a significant resistance per foot, or is there a way of making an electrical circuit to enable me to effectively drop ~5V across a sensor which is only 6 ohms in resistance?
RE: Circuit to make large voltage drop with small resistance change?
Look up 'milliohm circuit' to find some analog designs.
One trick for your back pocket is that, with the addition of a controller, you might be able to use a low duty cycle so that the measuring current is only applied a tiny fraction of the time (in case needed). This assumes that the level isn't changing too quickly.
RE: Circuit to make large voltage drop with small resistance change?
Thanks for the reply. Unfortunately I am restricted by my data acquisition equipment to measuring either a 0-10 vDC or a mili volt (thermocouple module) signal. I'm unable to measure resistance or current directly.
RE: Circuit to make large voltage drop with small resistance change?
What is the temperature of the metal? Most materials increase resistance as temperature increases.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
[IMG http://tinyurl.com/7ofakss]
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx
RE: Circuit to make large voltage drop with small resistance change?
You can't weigh the crucible?
RE: Circuit to make large voltage drop with small resistance change?
RE: Circuit to make large voltage drop with small resistance change?
This is going to be used in a permanent die Al casting. one set of probes will be cast into each casting to measure the fill rate. This is for a trial to characterize die filling. The probes are disposable and the fill time is short so the erosion of the probes should not be a problem. I can calibrate for the degradation of the probes. I can't weight the crucible or die as it is not practical. I believe i have all of the method and experimental design well thought out. My problem is measuring the signal with such a small voltage drop.
Although my voltage module in the DAQ can read 0-10V if i only get 0.1V voltage drop over the 1 foot length of wire then the noise in the system and lack of resolution will compromise the quality of the data. Having a 5-10V voltage drop would significantly improve the data. The problem with using a voltage divider is that the get a reasonable voltage drop the other resistor in the circuit would have to be 1-6 ohm. The resistance of any wire used in the circuit might be larger than this. I have also never seen a resistor made with this resistance magnitude. I have limited electrical experience so i might be wrong about these last two points.
The question is how can i obtain a significant voltage drop (>4v) with only a variation of 6 ohms of resistance?
RE: Circuit to make large voltage drop with small resistance change?
You've not stated what kind of DAQ you have, but many of them have strain-gauge amplifiers available, and such an amplifer would work fine in this setup. You could get fancier, and work your probe into one leg of a Wheatstone bridge (which is what a strain-gauge is), and have a loop of wire that is the probe, and a loop of wire outside of the die that is a reference leg.
Most resistor wire have a thermal coefficient, so the resistance measurement will be a mixture of both level and temperature.
RE: Circuit to make large voltage drop with small resistance change?
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
[IMG http://tinyurl.com/7ofakss]
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx
RE: Circuit to make large voltage drop with small resistance change?
IRstuff, Yes you are correct, however the I suspect that the noise from the power supply and other areas will have an effect. However i may try it and see what i get.
Thanks all.
RE: Circuit to make large voltage drop with small resistance change?
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
[IMG http://tinyurl.com/7ofakss]
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx
RE: Circuit to make large voltage drop with small resistance change?
RE: Circuit to make large voltage drop with small resistance change?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Circuit to make large voltage drop with small resistance change?
RE: Circuit to make large voltage drop with small resistance change?
https://www.emf-corp.com/copper-slides.html
RE: Circuit to make large voltage drop with small resistance change?
David Stonier-Gibson
http://splatco.com