uni-t UT682 wire tracker some output oscilloscope measurements + cable finding   - Page 1
Forum section: electronics / general

author: Dip_Switch
author_rank: Newbie
timestamp: January 25, 2022, 12:15:33 am
content: Hi EEVblog.I recently made some oscilloscope measurements of the transmitter output ofa uni-t UT682 wire tracker.I am interested in modifying the little thing to a have a real wire finder/detector/scannerfor 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 OhmTransmitter output resistance calculated Rout (Load 50 Ohm) = 179 OhmNo Load output Vrms=4.41V100 Ohm Load output Vrms=1.61V Irms = 16.1mA50 Ohm Load output Vrms=0.961V Irms= 19.2mARout = R_load * (U_no_load/U_load -1)Transmitter output resistance, no battery, switched off: 9,1KOhm = DC coupledAdding something like a BUF634 current amplifier (250-mA High-Speed BufferPin-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 capacitorplus 6m single wire (in closed loop mode) as the load.Irms = 57mA Vrms =2.6818 ṼI 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 endof 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 = Gndpins counted from left to right looking at the RJ11 pins on top, cable showing away from bodyUT682 Receiver :For Ethernet lan cable/ port detecting it is quite sensitive. You have a good chance to detectnot 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 onmy 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 frequencycompare the induced voltages : 4A/50Hz to 450khzU_ind_450Khz = U_ind_50Hz * 450000/50 = U_ind_50Hz * 9000The other way around: If your B field sensor is happy with the 4A/50Hz magnetic fielda frequency independent sensor should be happy with the magnetic field producedby 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.apkAC Live Wire Finder_v1.1.xapkAC Magnetic Field Meter_v1.03.apkMagnetic Tool_v2.5.0.apkUltimate EMF Detector RealData_v2.9.4.xapkWire Metal Detector_v1.03.apkWire Pipe Locator_v15.0.apkBut 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 longerHappy Gold, Diamond, Opal or cable finding!Greetings.Dip_Switch