Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Help with KEPCO power supply used as AC amplifier

Shotky

Newbie level 4
Joined
Mar 17, 2021
Messages
6
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
70
Hello everyone!


I am trying to obtain the phase relation between the output voltage of a pick up coil (wound coil of 150 turns), when inserted into a variable magnetic field, and the filed excitation current.

This field is obtained from an alternating excitation current that flows into a wire loop, the pick up coil is placed at the center of this current loop.
The excitation current is obtained from a KEPCO 72-6m power supply/amplifier, used in current mode and controlled with a sinusoidal waveform at fixed amplitude and with frequency in the range 100Hz- 100kHz, obtained from a waveform generator.

Current excitation and coil output voltage signals are acquired with a DAQ board; the coil is connected to the DAQ analog input in floating source configuration with a 20 m long twisted pair cable, the excitation current is obatained from the voltage drop on a shunt resistor (50m ohm).

what I obtain is in the attached files: the difference between coil voltage phase and excitation current phase is not in a range of 180 degrees, anche it seems that the peak resonance in the amplitude plot ( ration of V amplitude anche I amplitude) is not at the same frequency of the resonance in phase plot.

Can someone please help me understand what I am doing wrong?
 

Attachments

  • Measured_bode_plot.png
    Measured_bode_plot.png
    68.1 KB · Views: 33
  • circuit-3.png
    circuit-3.png
    51.4 KB · Views: 35

BradtheRad

Super Moderator
Staff member
Joined
Apr 1, 2011
Messages
14,240
Helped
2,817
Reputation
5,642
Reaction score
2,757
Trophy points
1,393
Location
Minneapolis, Minnesota, USA
Activity points
106,227
Strange as it seems the blue plot is correct (in purely mathematical terms) to have that abrupt jag at the point where it changes between +180 and -180 degrees. Even though it disturbs our sense of continuity.

It's not clear from your schematic whether the pickup coil is: (a) a continuous loop (zero or low ohms), or (b) a coiled length of wire (infinite ohms). The wiring also is unclear how your reading is taken from it.
It could make a difference in the phase relationship. In case A the time constant is long, in case B it's very short.
Inductive time constant formula: L/R
 

Shotky

Newbie level 4
Joined
Mar 17, 2021
Messages
6
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
70
HI,

thanks for the help.

the pick up coil is made of 150 turns, R=767 ohm, L=76 mH, it has twisted pair cables that I connect to the analog input of my DAQ as floating source
 

Attachments

  • pick_up.pdf
    15.6 MB · Views: 2

BradtheRad

Super Moderator
Staff member
Joined
Apr 1, 2011
Messages
14,240
Helped
2,817
Reputation
5,642
Reaction score
2,757
Trophy points
1,393
Location
Minneapolis, Minnesota, USA
Activity points
106,227
From the looks of your setup you're taking a reading of voltage across the pickup coil itself. Yet little or no current flows through it.

To see a phase change, current must flow in an inductor. But you can't read current by taking a direct volt reading across the leads of the inductor. The usual method is to measure voltage across a resistor installed in the path. (Current through a resistor automatically generates a voltage across the resistor, proportional to Ampere level.)

Therefore I believe you'll get success by installing a resistor across the ends of the pickup sensor. The amount of phase change is greater with less resistance. Try a low-ohm value although high enough ohms so that you can take a usable reading.

Also try tilting the pickup coil in different directions, to see how its orientation affects how much it's influenced by the sending coil.
 

Shotky

Newbie level 4
Joined
Mar 17, 2021
Messages
6
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
70
Hi,
thanks for the help.


Actually I want to obtain the phase difference between the coil output voltage and the excitation current in the outer loop (coming from Kepco amplifier in current mode).
For this reason I used a shunt resistor in series with the current loop (source) to obtain a voltage drop and from this the excitation current
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
49,166
Helped
14,395
Reputation
29,054
Reaction score
13,145
Trophy points
1,393
Location
Bochum, Germany
Activity points
283,351
At 100 kHz both measurement channels have probably phase errors, there's nothing strange about the measurements provided in post #1. You would need to calibrate the setup before making conclusions.

What is causing the sharp resonance in the excitation current?
 

LaTeX Commands Quick-Menu:

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top