uni-t UT682 wire tracker some output oscilloscope measurements + cable finding

[Dip_Switch]

Hi EEVblog.


I recently made some  oscilloscope measurements of the transmitter output of
a uni-t UT682 wire tracker.

I am interested in modifying the little thing to a have a real wire finder/detector/scanner
for in earth cable, in/under plaster/ in concrete  cable finding  under 400V AC.
Do not try this with the unmodified UT682!

If someone is interested in its transmitter output signals, this is for you.


UT682 Transmitter :
Transmitter output resistance calculated Rout (Load 100 Ohm) = 173 Ohm
Transmitter output resistance calculated Rout (Load 50 Ohm) = 179 Ohm
No Load output Vrms=4.41V
100 Ohm Load output Vrms=1.61V  Irms = 16.1mA
50 Ohm Load output Vrms=0.961V Irms= 19.2mA

Rout = R_load * (U_no_load/U_load -1)

Transmitter output resistance, no battery, switched off: 9,1KOhm = DC coupled

Adding  something like a BUF634 current amplifier  (250-mA High-Speed Buffer
Pin-selected bandwidth: 30 MHz to 180 Mhz) or any other eventually plus OPA810 plus +/-15V power supply would result in a more powerful transmitter. 

I tested this with 2 parallel  BUF634Ts with  47 Ohm output resistor  plus a 33nF capacitor     
plus 6m single wire (in closed loop mode) as the load.
Irms = 57mA  Vrms =2.6818 Ṽ

I could detect  the wire over air  in a distance of 1-2m.
In open loop mode  = only the signal line of the transmitter connected to one end
of the wire, the wire almost in a straight line on the floor, detecting distance was a bit reduced.
I found the results promising and a lot better than without the BUF634 current amplifier.   
Each advance comes with a disadvantage. So: A transmitter needs a good stepless current/voltage control and some power (horses) to be controlled.


RJ11 alligator adapter pins:  pin2/red = signal   pin3/black =  Gnd
pins counted from left to right  looking at the RJ11 pins on top, cable showing away from body

UT682 Receiver :
 
For Ethernet lan cable/ port detecting it  is quite sensitive.  You have a good chance to detect
not 63 lan cables but 1 single. But the UT682 output current is limited to 25mA (I think I found this value in one of the uni-t manuals as maximum output current). I did not test the short circuit behaviour.....  Eventually there is a ptc fuse or whatever... in the end I will add some form of current amplification...   
-Does not react on a 7.4A loaded AC 50Hz power line. Reacts on switched power supplies.
-Not PoE active scan enabled.  Be careful here. I did not test this. 


Basic ideas:  Before I had the ut682 I was trying some wire / pipe finding /EMF .apk's on
my  Galaxy smartphone. I found out that the B field  in my rooms is in a range of 44 µTesla.
Then I calculated something like: If  you  generate  a 4A DC/AC  current in a 3 wire power line (US jargon Romex or so) I would  expect a magnetic B field of  1-2 µT in a distance of 5cm from the multi wire power line if forward and backward = 2 wires are used. Using just one wire I would expect a magnetic field more in a range of 20 µT.  AC creates eventually more interference because   d/dt  of the magnetic flux integral  does not equal 0. Frequency influence: What could be the best frequency for the job? Answer: I do not know. Fluke uses 125Khz. If my memory serves me well. Induced Voltage  is proportional to d/ dt  e^(j*2*Pi*f*t)....f = transmitter frequency

compare the induced voltages : 4A/50Hz to 450khz
U_ind_450Khz =   U_ind_50Hz * 450000/50   = U_ind_50Hz * 9000
The other way around: If your B field sensor is happy with the 4A/50Hz magnetic field
a frequency independent sensor should be happy with the magnetic field  produced
by a 450khz signal and a current of 4A/9000 =    4.4*10^-4 A = 0.44mA.
Using a receiver coil  or so... 
   
Smartphone 3 axis Hall sensors have sensitivities around 0.3 or 0.6µT.
Having a switchable load 200-1500 Watt AC(6-7 position switchable hotplate or so, hot air gun etc.  ) for a smartphone apk based  cable finder is not the worst idea I ever had = working.
You should have a load control in one or the other way.
Old 2500Watt AC triac  power control  I use for power tools without RPM poti or whatever.
Not the most sophisticated way but eventually working.

     
used apks:

AC Live Wire Detector_v1.0.apk
AC Live Wire Finder_v1.1.xapk
AC Magnetic Field Meter_v1.03.apk
Magnetic Tool_v2.5.0.apk
Ultimate EMF Detector RealData_v2.9.4.xapk
Wire Metal Detector_v1.03.apk
Wire Pipe Locator_v15.0.apk



But this is no solution for non power lines.

If you find  typos or denglish....
Spread the cloak of secrecy and oblivion over it.

I am waiting for parts from china. China has new years festival...waiting longer

Happy Gold, Diamond, Opal or cable finding!
Greetings.
Dip_Switch