Magnetic Sensors

[barkingspider]

The current project I am working on has run into some issues with a magnetic environment sensor. I was wondering if anyone had some tips that might point me in the right direction to help solve this. We have a simple magnetic sensor that is roughly 1” in diameter and about 1” long. It is composed of a magnet with a copper wire coiled around it, potted into a metallic housing. The copper wire runs to 2 pins that leave the housing. The sensor is used to detect a change in environment. This particular environment is a metallic barrel which the sensor travels down and exits from. The sensor travels down the barrel at a high velocity. Flux is constant as the sensor moves within the barrel, when it exits, a change in flux occurs. This induces EMF in the sensor coil that produces a voltage. This voltages passes to a circuit that detects the voltage. The problem we are having is that the sensor is generating too low of a voltage. We are trying to determine what factors determine the voltage that is generated and what we need to do to increase this voltage. The reason I’m asking is that I can’t seem to find any sources that have information in this specific area. The sensor is traveling at roughly 700 m/s and there seems to be very little information out there on high speed flux change. The major factors that determine the voltage I know of include: Magnetic Strength, Sensor Velocity, Air Gap, Sensor Resistance, and Sensor Coil Inductance. Other than barrel design, what might be altered to increase the voltage?

Brian
Pro/E Mechanical Design & Checking
Aerospace and Defense
Florida, USA

 

[BobM3]

Number of windings in your coil would be one. Also try to get the flux directed in such a way as to maximize the flux density crossing the windings.

 

[IRstuff]

Magnetic coils are determined by the number of turns on the winding.

How long is the pipe/cable?

Why not send a Hall effect sensor down?

TTFN

FAQ731-376

 

[Clyde38]

All things being equal except:
Stronger magnet - increased voltage
Higher velocity - increased voltage
Smaller air gap - increased voltage
Sensor resistance and coil inductance as it relates to the number of turns, more turns - increased voltage
Lower temperature - increased voltage

And try this link:

http://books.google.com/books?hl=en...et93AU&sa=X&oi=book_result&resnum=3&ct=result

 

[barkingspider]

BobM3 & IRstuff. Thanks for your reply....we have tried increasing coil windings from 182 turns to 275. No significant voltage increases were seen. We believe that at these high velocities the affects of increasing coil winding is minimal, based on the data we have seen.

The barrel is roughly 30ft and the environment in the barrel is such that a Hall Effect Sensor would probably not survive.

Brian
Pro/E Mechanical Design & Checking
Aerospace and Defense
Florida, USA

 

[IRstuff]

How exactly are you sensing the change?

Given the structure, one might think that it has a resonant frequency, and an excitation at that frequency would show the greatest impedance change.



TTFN

FAQ731-376

 

[IRstuff]

Doing your signal conditioning while including 30ft+ of wiring is not going to help

TTFN

FAQ731-376

 

[barkingspider]

Thanks guys. The sensor is integral to the device being sent down the barrel, so there is not a 30ft cable. The sensor, as part of the device, sits close to the barrel wall in the barrel and upon acceleration and exiting from the barrel into air, a voltage is generated. The voltage data from the event is captured electronically and retrieved after the event. We have modified the the number of coils, among other controlled variables to increase voltage, however the data we've collected thus far suggests a plateau, where at very high speeds, the sensor becomes saturated and cannot increase voltage to the value we are calculating. One of our engineers is investigating a phenomena called flux diffusion that may be not only related to the internal sensor geometry, but also the high speeds at which we are traveling down the barrel prior to exit.
Thanks for your all your inputs.

Brian
Pro/E Mechanical Design & Checking
Aerospace and Defense
Florida, USA

 

[dgallup]

What is the barrel material?

 

[barkingspider]

Barrel is 1010 steel, magnet is Alnico VIII HE

Brian
Pro/E Mechanical Design & Checking
Aerospace and Defense
Florida, USA

 

[IRstuff]

Why wouldn't it simply be eddy current?

http://en.wikipedia.org/wiki/Eddy_current

TTFN

FAQ731-376