Go Back   Physics Help Forum > College/University Physics Help > General Physics

General Physics General Physics Help Forum

Like Tree1Likes
  • 1 Post By studiot
Reply
 
LinkBack Thread Tools Display Modes
Old May 9th 2018, 07:32 AM   #1
Junior Member
 
Join Date: May 2018
Posts: 1
Red face Help Signal Attenuation

We have a question we cannot understand…

We are university students working on a pet project, we are trying to pick up an electrical current passing through a conductor via a capacitive sensor (i.e. attached to a charge amplifier with filters) that is not in direct contact with the circuit.

The signal we detect seems to be larger when the conductor is in contact with one electrode only.

As soon as the circuit is completed (we connect the conductor at both ends) the signal we detect on our sensor is either attenuated or disappears altogether…

The signal source is a battery powered generator with no direct connection to the sensing circuit. We are simply trying to detect an electric field.

The signal is about 2 volts over 0.45ms

Does anyone know why this is or what is happening?

Any help really appreciated...
thepadct is offline   Reply With Quote
Old May 9th 2018, 08:05 AM   #2
Senior Member
 
Join Date: Apr 2015
Location: Somerset, England
Posts: 995
This is common.

What do you see on an oscilloscope with a trailing length of wire connected to the input?

Nowearth the other end of the wire.

Again what do you see?


In the abscence of a resistive load the scope input will pick up random RF signals, perhaps even tens of volts since the everage electric field in a room may be several volts/metre.

You need a resistor across the input of your measuring device to 'settle' the input.
topsquark likes this.
studiot is offline   Reply With Quote
Old May 10th 2018, 10:39 AM   #3
Senior Member
 
Woody's Avatar
 
Join Date: Jun 2016
Location: England
Posts: 642
Am I correct in surmising that you are simply placing a wire across the terminals of the signal generator?

Is your signal generator "happy" to work with a dead short across it's output terminals?
__________________
~\o/~
Woody is offline   Reply With Quote
Reply

  Physics Help Forum > College/University Physics Help > General Physics

Tags
attenuation, signal



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Photon energies and attenuation Chris2093 Nuclear and Particle Physics 2 Nov 17th 2016 01:51 AM
Attenuation and Packing in hydraulic Transients mikealvarado100 Thermodynamics and Fluid Mechanics 0 May 13th 2016 01:14 PM
attenuation of electromagnetic wave in metal problem pranimaboity2050 Advanced Electricity and Magnetism 0 Dec 11th 2014 12:21 AM
NMR Signal Question Help Needed! johnq2k7 Advanced Electricity and Magnetism 0 Oct 13th 2009 06:52 PM
signal image processing noor Advanced Waves and Sound 4 May 2nd 2008 02:37 PM


Facebook Twitter Google+ RSS Feed