Here we go again Joe. I'm trying to wrap my head around this so hopefully I'm not wearing your patience thin...
The DMM has a high input impedance and therefore should have minimum impact (meter loading?) on the measurements I was taking on the secondary of the Hammond Isolation transformer - right? Therefore the result was the voltage readings of 72 V and 20 V.
The analog meter with it's lower input resistance would have an impact on the measurements and act as a load - right? Thus I got the 0 volts reading.
After reading the information below am I on the right track? Without a substantial load on the secondary of the transformer the voltage readings I am getting with the DMM are a result of, and I quote, "under lightly loaded conditions, the reactive drop may not provide sufficient voltage reduction, or attenuation"???
I have lots of patience for people who give a darn and are willing to take the time to figure things out!
That said, your last attachment is leading you down the wrong path. That material is letting you know that harmonics, noise, and transients, that wouldn't typically have much amplitude in a normal load impedance, can create problems with a high load impedance. Again, the ratio of impedances comes into play. Your source 50 or 60 Hz power should have an extremely low source impedance, while the harmonics and noise should be a hi-z source. But if your load z is high, you might see close to the same amplitude on the secondary.
You're dealing with more like what we consider "parasitics" in electronics. You showed a description of a shielded isolation transformer. Think of a twisted, shielded cable Vs a non-shielded twisted-pair cable. The pF/foot is much higher on the shielded cable so although you have more noise immunity, you suffer more high frequency attenuation. Your transformer probably has a greater amount of capacitive coupling between the secondary Neutral and the grounded case. You should draw a resistor, a cap, and an inductor, between each leg and ground. Then draw a voltmeter symbol to represent your DMM, and another for your Weston. Then write down the input resistance and capacitance for each. All of the Rs and Cs and Ls make complex voltage dividers that cause readings like the ones that you're getting.
A ground detector is there to detect grounds, not to protect from getting shocked. It actually creates a path that may or may not limit currents to a safe level.
Joe
