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    Which one is correct?

    Well, that didn't work....





    Tom
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    #2
    Click image for larger version

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    M1 M2 M3 M4

    M2-M4 are connected from Hot of GFCI receptacle to tank of water heater.
    M1 is connected between WH tank and preheat Storage Tank.

    Click image for larger version

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ID:	2543425 M4 only


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    Tom
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      #3
      Why can't they all be correct?

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        #4
        Click image for larger version  Name:	m3.jpg Views:	0 Size:	133.8 KB ID:	2543436Click image for larger version  Name:	m4.jpg Views:	0 Size:	123.3 KB ID:	2543437

        Meter 3 only...…………………………………………………………... Meter 2 Only

        The goal is to show how different meters will give different results for the same problem. How the impedance of the meter makes a difference.


        A couple more to go..
        Tom
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          #5
          Click image for larger version  Name:	m5.jpg Views:	0 Size:	78.2 KB ID:	2543443Click image for larger version  Name:	m6.jpg Views:	0 Size:	143.0 KB ID:	2543444

          All of them.............................................. .......................................and then some complications.

          I only want the top two...


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          Tom
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            #6
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            The original voltage checks of one meter at a time referenced the far left section of pipe. It and this storage tank is isolated except for whatever conductivity the water has. Notice the high impedance M1 now shows 5 volts between the tanks.
            The ''complication voltages are the results of the M2, being placed on the fitting near the wall. The far left is M4 with M3 in the center.



            Tom
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              #7
              Just to check, I’d like to see the readings with fresh batteries.
              we see odd readings on ours with weak batteries. I know the dummy icon isn’t on to tell you the battery is low.
              neither are ours....
              when we get odd readings, we change batteries no matter what icon is showing.

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                #8
                191107-2436 EST

                ptonsparky:

                I really don't understand your experiments and results.

                I need one experiment at a time, and a precise definition of the conditions.

                If AC measurements are made along a low resistance conductor that has a high current flow, then the measuring loop may see a substantial induced voltage from that current that may produce a large error in the intended measurement. A foot or so of copper water pipe with 10 A flowing thru it won't show much voltage drop. To get a 5 mV drop at 10 A requires the resistance to be 5/10,000 ohm. #10 copper wire is 1 ohm per 1000 ft, or 1/1000 ohm per foot. I estimate that 1/2" copper water pipe is about 1/10 that of #10 copper wire. Or the water pipe would be about 1/10,000 ohms for 1 foot.

                .

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                  #9
                  Originally posted by Hv&Lv View Post
                  Just to check, I’d like to see the readings with fresh batteries.
                  we see odd readings on ours with weak batteries. I know the dummy icon isn’t on to tell you the battery is low.
                  neither are ours....
                  when we get odd readings, we change batteries no matter what icon is showing.
                  Been there. It is the reason I have two of the 87s. I thought the first had gone toes up before I noticed the battery symbol.
                  The 87s I checked to see if the batteries were up and the other two I knew were within the last couple months.
                  Tom
                  TBLO

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                    #10
                    The first picture shows M2 to M4 all connected to a grounded/bonded tank of the water heater. Each shows relatively the same voltage. M1 shows the voltage between the floating storage tank and the WH tank.

                    Each subsequent single meter test shows the voltage to the floating ST, with M1 showing what the voltage between tanks is raised to as each meter is tested.

                    later...
                    Tom
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                      #11
                      Using a wiggy type tester between the power and the floating ST would probably have shown nothing but the ST to HWT voltage would have gone up to the 124. I don't have one that I use.

                      Placing two of the T+ in parallel dropped the voltage reading to about 12 volts. Not shown.

                      The meters all showed the correct voltage in the context that they were used, but voltage to a floating piece of cu pipe, or anything else is meaningless.

                      Tom
                      TBLO

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                        #12
                        Do a search for >voltmeter ohms per volt<. The impedance of the meter makes a difference! I remember one of my professors mentioning that 1970s era voltmeters were usually 20,000 ohms/volt. He added that earlier voltmeters had a lot less resistance (impedance?), and that some circuit diagrams for electronic things had notes that 'volt readings are with 1000 ohms/volt meters' or some such, as the quote, below, explains.

                        Quoting from AntiqueRadios.com (https://www.antiqueradios.com/forums...php?t=129660):
                        1000 ohms per volt, if you do the math (Ohm's Law, E/R, 1/1000) is equivalent to 1mA. 1mA was the standard range for a panel meter in the days before alnico magnets, so all the radio VOMs were 1000 ohms per volt, and the schematics and voltage tables were written with that assumption.

                        In the late 30s, when alnico became available, 50µA meters were possible, which translates to 20,000 ohms per volt.

                        If you have a meter that draws 50 microamps, but want it to draw 1 milliamp, you just shunt it with a suitable resistor.

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                          #13
                          The analog Sympson meters were nice. If the needle stayed in relatively the same portion of the meter as you changed scale you knew the voltage reading was bogus. Ghost Voltage is what the term is now. It changed the ohms/volt.

                          Tom
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                            #14
                            Originally posted by gar View Post
                            191107-2436 EST

                            ptonsparky:

                            I really don't understand your experiments and results.

                            I need one experiment at a time, and a precise definition of the conditions.
                            Exactly! I have no idea what that mess is about other than you are trying to show how differences in input impedances cause errors.

                            -Hal

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                              #15
                              Originally posted by hbiss View Post

                              Exactly! I have no idea what that mess is about other than you are trying to show how differences in input impedances cause errors.

                              -Hal
                              I agree, it’s a mess...

                              That and taking a voltage measurement to some floating object means nothing, other than the impedance differences stand out.
                              Tom
                              TBLO

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