Hi,
I am using a Fluke processmeter 789 and a Fluke 187 True RMS meter. The transformer is running at 50Hz. I don;t quite understand what you mean by siemen range. Can elaborate. Yes it pure AC without any rectification.
On the 187 when you set the selector switch to ohms, you will see above the Ω symbol, in blue, the designation "nS". That means nanosiemens (which is a measurement of conductance, instead of resistance. Conductance is the reciprocal of resistance). After selecting ohms, press the blue button twice to enter the nanosiemens range.
Using the ordinary probes, connect them to the tip of the HV probe, and the banana plug that goes into the jack on the far right, where normally your red probe goes. The reading will be slow to settle down, but eventually it should reach a value of 1.00 (plus or minus probably 10% or so), which is equivalent to 1000 megohms (1 gigaohm). I think the HV probe you have has a 1000 megohm multiplier resistor inside. If not, then this technique will give you a mesurement of its actual resistance. You should be able to find out what the intended resistance of the internal multiplier is from the spec sheet of the HV probe.
If you plug both banana plugs of the HV probe into the 187 while in nanosiemens range, with the ground clip of the HV probe not connected to anything, the reading should approach zero (more probably 0.01 which is 100 gigaohms); there's not supposed to be much leakage between those two banana plugs.
It occurs to me that if you have the HV probe connected to the 187 in the normal way to make a measurement, you could connect the ground clip to the probe tip, and with the 187 in nanosiemens range, you would see the value of the internal multiplier resistor (in nanosiemens, of course).
Since you have two meters, for a really definitive check, you could connect the HV probe to the 187, and measure your voltage with the 789 directly at the same time as you use the HV probe on the 187. Then you have a known good reading from the 789 to compare with the HV probe reading at the same time.
Perhaps the 80K-40 isn't specified to work with AC.
Even if the HV probe isn't specified for AC, you can use the two meter trick I just described to determine a calibration factor for the HV probe when measuring AC volts, which you can then use for higher voltages if need be.
While making the simultaneous readings, divide the 789 known good reading by the HV probe reading. This gives you a factor by which you can multiply a subsequent HV probe reading to get the actual voltage (which might then be greater than 1 kV) being measured.
Also, once you have both meters making the measurement, using the HV probe on the 187, watch the reading on that meter (the one with the HV probe) when you disconnect the other one, and see if the reading changes. This will tell you if the 10 megohms input impedance of the 789 is loading your circuit significantly.