For the F27, you could for example, try using the AC line to get the PTCs to switch, then quickly attach it to the calibrator. Maybe just a DPDT switch to prevent it from cooling.
The calibrator is now up to snuff. It will put out more current at lower voltages, up to about 250 volts, above that it is limited to 8-10mA continuous. For the F27, when I monitor current, I can see that the PTCs do take some time to heat up, they don't 'switch' quickly at all. At 250V it is 'over the hump' so to speak, but the huge PTC in the F27 is still beyond what the calibrator can handle in one go. If I give it a 1000VAC jolt cold, the current goes to a bit over 20mA, as would be expected given it's ~4.6K cold combination of the 3.5K resistor and PTC--but this is too much current and the calibrator trips off. The two series PTCs of the F116 are a bit easier for it, but even at 600V the current takes some time to settle. Anyway, I can now energize both meters at their rated voltage, although the F27 has to be brought up in stages.
I assume these are all after the PTCs have switched. Otherwise for LowZ, I would expect the current to be much higher. At a kHz, I doubt you will see much change.
Well, there's the problem--it does change, and a lot. I tested them at low and high voltages with different frequencies. I used 6V and 600V for the F116, then 15V and 1000V for the F27. I needed to use the higher voltage on the low end for the F27 because it doesn't have a Lo-Z mode, so I have to overwhelm the low voltage clamps in whatever circuit I'm using (OHMS in this case) so that I see mostly the PTC/resistor characteristics.
At 6VAC in 'AUTO V/Lo-Z', the F116 had a current of about 2.0mA @ 50Hz, and that didn't change much at 1kHz or even 10kHz. However, at 600VAC, it had about 1.9mA at 50Hz, but that rose to 5.1mA @ 1kHz.
The F27 at 15VAC stayed in the 2.1-2.3 range, not totally steady because the OHMs circuit was reacting a bit. At 1000VAC, it showed about 2.0mA @ 50Hz, but raising the frequency to 1kHz caused a surge to about 7mA and then it settled back down to 5.4mA.
Those are huge differences from 50Hz to 1kHz, but only at higher voltages. I have to wonder if the trend would continue if you kept going--the calibrator is maxed out. I'm only at 10
6 V-Hz but some of these meters are supposedly good for 10X or 20X more. The next time I place an order maybe I'll get a few of those big dark grey monster PTCs that you find in the larger CAT III/1000 Flukes and try to characterize them. It looks like they pick up 500-1000pF when they warm up. Maybe they should be called thermisto-varactors.