The picture that shows it 'slipping under' - Big goof.
The finger goes in front of the large step flange.
The flanges and bumps along the way are impedance pathways - leakage currents
Consider the probe good for 50KV or there abouts.
a 20,000 ohm/volt meter was used with them - so you have a 1000x probe.
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Pete C. wrote:
** According to the third post down - it is 50 kV and 1000 megohms.
Will give readings about 5% low with a 10 meg DMM.
Easily checked and calibrated.
Thank you Phil. I will make sure to multiply my readings by 1.05. I
appreciate your help.
I just tried this probe to measure house mains AC voltage.
AC voltage (real): 251 V
Reading using my probe: 0.55V
That would suggest that when measuring with the probe, I need to
multiply my readings by about 251/0.55 = 456 times, to get the actual
Is that the right calculation?
** Something is wrong.
1. Test the resistance across the twin plug with your ohmmeter - should be
about 1 megohm.
2. Make sure the twin plug in inserted in your DMM the right way around.
3. Find a source of DC voltage and compare readings with and without the
Yes, it is strange. I tried measuring DC from a military surplus power
With multimeter: 127.1
With probe: 0.130
So, with DC, the probe gives a 1:977 reading,
I am not sure how it could be so different with AC.
In any case, I will need to measure DC.
** Think about stray capacitance.
Note how a 10:1 scope probe has to be adjusted to match the scope input to
avoid HF response errors.
Maybe adding the right value cap across the twin plug pins will fix your
Try 22 pF for a start.
High voltage mica or ceramic of course !
Very few meters really have anything close to 10M impedance for the AC ranges.
Even a HP 34401 is as low as around 2.5M in the AC ranges. I use a Leader AC
millivolt meter with a Fluke proble for AC readings. Vacuum tube voltmeters
would be suitable as well.
The design specifications are only as accurate as the manufacturing
practices used to build the item. Component values and insulation
specifications will drift with aging.
The HV-211 HV probe is for use with a voltmeter having a nominal DC
voltage input resistance of 22 Mohms.
Beckman was a quality manufacturer, and their test equipment was
considered to be some of the best in terms of dependability.
Beckman Industrial instruments, later sold/licensed to Emerson
Electric, later operated under Beckman again, later absorbed into
Design specs are generally accurate when the equipment is new, or
within a reasonable service lifetime.
I generally consider the reliability of an aged, used instrument or
accessory to be zero, since the history is completely unknown.
Until all internal component values are verified, one wouldn't know if
components have been abused, damaged, improperly repaired/altered, or
substituted. I don't rely on any used test equipment until I've
confirmed the performance with reliable equipment.
The Beckman HV-211 is likely to be about 25 years old.
(from the Beckman specification/instruction sheet)
Voltage rating: 0 - 50,000 VDC
Input resistance: 1000 Mohms nominal
Division ratio: 1,000 to 1
Accuracy: (with 22Mohm meter load) +/- 2% at 25kV changing linearly to
+/- 8% at 50kV and 1kV.
Maximum input: 50kVDC or peak AC
Operating conditions: 0 deg C to 50 deg C, 0% to 80% RH
The internal components of the particular version of the HV-211 that I
have, have marked values of 955 Mohm 1% HV resistor assembly (actually
2 joined, large ceramic-bodied HV resistors) and a 1 Mohm 0.25%
resistor across the meter terminal connections.
I own this probe, bought new in April 1981, and so have the Operator's
Manual, a single sheet.
The max voltage is 50 Kilovolts, AC or DC.
It was intended for checking the acceleration voltage on CRT tubes.
It is a 1000:1 divider, designed to work into a 22 Mohm load.
Accuracy on DC +/- 2% up to 25 KV, dropping to +/- 8% from 25 KV to 50
KV. AC won't hurt it or the connected meter, but no accuracy is claimed
for AC use.
That's great. I have actually a question about its hookup. Does it
kind of assume that one side is grounded potential? That it is "safe"
to clip the alligator to one of the ends? And then the other end is
"dangerous" and high voltage relative to ground, that should only be
touched by the tip of the probe?
And if I make some sort of a pulse discharge system, is it safe to
ground one side of it, or would it be able to somehow pass possibly
harmful oscillations to ground?
Thanks Joseph, that was supremely helpful. I now feel very good about
using this probe.
It does not assume anything. It's just two resistors in series, built
into a HV probe case. The resistor from probe tip to output pin is 999
Mohms, and the resistor from output pin to ground is 1 Mohm.
Output pin and ground are wired to the banana plug that goes to the
Ground is also wired to the alligator clip lead.
So, if the probe is at high voltage and the ground clip is connected to
circuit ground, the output pin is at 0.001 times the input HV.
If that ground clip comes loose, the whole affair is at HV, but through
a 1,000 Mohm resistor.
The probe is just a big resistor. Hook it from HV to ground and don't
worry about oscillations. Nor can you hurt ground with "harmful
oscillations", or anything else.
(1 microfarad)(10^9 ohms)= 1,000 seconds to get to ~1/3 voltage. This
will drain the HV capacitors, but very slowly, and maybe not completely.
After the voltage stops dropping, connect a much smaller resistor across
It should work just fine for measuring the charge on a HV capacitor.
Although the probe is (was) calibrated for use with a 22 Mohm meter,
anything from 10 Mohms up should work just fine, perhaps with a slight
error (~5% at 10 Mohm)) due to slight added loading of the 1 Mohm leg of
the voltage divider within the probe.
Welcome. But please make sure that the ground clip is quite secure, as
if it comes off, your voltage readings will be way low, which could lead
to a surprise. It's useful to have a calibration source handy: A
100-volt source will read as 100/1000= 0.1 volts, which is easily
measured with a digital multimeter. At 22 KV, trust nothing.
What I mean is this: suppose that I have a HV system, such as a
charged capacitor bank, such that one side is grounded and another is
charged at high voltage.
Suppose also that my body is grounded.
I can measure voltage in two ways:
1) Clip the alligator clip to ground and touch HV side with the pointy
end of the probe
2) Clip the alligator clip to HV side and touch the ground with HV
Clearly, 2) is dangerous since my hand, holding the alligator probe,
would be almost touching the HV side.
Whereas 1) is not dangerous, as far as I can tell.
If so, then, this probe can be used on HV systems where one side is
grounded, in only one way.
This all may sound obvious, but I want top be very redundant in making
sure that I use it properly.
You should run with the cases at a low potential (ground), connect the
"hot" end of the probe to the HC terminal on the cap, the alligator clip
to the case of the caps, and the other ends to your meter, with the
meter set to the right voltage scale.
Once you have made all of these connections, do NOT touch anything
(including the probe OR meter) while there's high voltage on the caps.
Do NOT manually "probe" the caps while they are charged. A failure in
the high voltage resistor can lead to some nasty problems - and you
don't want to be near (or part of) the discharge path if this should
We specialize in UNIQUE items! Coins shrunk by huge
And the insulation on the alligator clip is nowhere near good enough to
hold off 22 KV, which can jump an inch in dry air.
Approach 2 is more than dangerous, it's sure to kill.
Yes. The alligator clip goes to ground (~earth). Period. But make it
The problem with probing is that one's hand can slip. With a TV tube,
the stored energy probably won't kill. A 1 mike, 22KV capacitor is
quite another thing. There are no second chances, even for cats.
I would wire things up with no HV, then creep the power up with a variac
and see how it goes, without touching anything, then disconnect power
and walk away for an hour.
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