Readout pin on oscilloscope probes

You talking about that small pin that is part of the BNC connector? If so, it's function is simple, it connects to ground when in the 10X mode, IIRC.

PeterD schrieb:

Yes.

Thanks (I expected it to be more complicated though).

Does that mean it's just disconnected in X1 mode? What about X100?

Philipp

Philipp Klaus Krause wrote in news:4a2c1c42$0$29137$ snipped-for-privacy@read.cnntp.org:

try

--
Jim Yanik
jyanik
at
kua.net

Many of these probes have a resistor between the read-out pin and its ground. And in case of some Tektronix scopes, they use this resistor and scope's internal resistor to form a voltage divider to devide some know internal reference voltage. They look at the divided voltage to determine the type of probe connected.

Since I had nothing better to do this afternoon at work, I decided to measure this resistance for probes around me. So the following table was made.

Probe Series R Type Readout R

----------- -------- ------ ---------------------- TEK P6053 9M x10 INFINITY TEK P6062B 360/9M x1/x10 INFITITY/12K TEK P6106 9M x10 11K TEK P6130 9M x10 11K TEK P6131 9M x10 11K TEK P6137 9M x10 11K TEK P6138A 9M x10 11K TEK P6139A 9M x10 11K HP 10073A 900K x10 11K HP 10441A 900K x10 obviously zero(3-1ohm) LeCroy PP062 500 x1(?) 11K

This is why when I connect LeCroy PP062 to Tek scope, it thinks it's a x10 probe, but actually I get ten times bigger waveform.

Then I became even more curious. So I used bunch of 1K ohm and other resistors to "test" how Tek scopes judge probe types based on this resistance. To my surprise, somewhat modern TDS684B distinguished 7 different probe types including x1 as default. Following table is the result.

Readout R TDS684B 2465DMS

--------- ------- -------

11k x10 x10 10k x10 x10 9k x10 x10 8k x10 x100 7k x100 x100 6k x100 x100 5k x100 x1000 4k error x1000 3k x2 x1000 2k x5 x1000 1k x200 x1000 510 x1000 ID mark

I've never seen x2, x5, x200 or x1000 probes myself, as well as I'm not sure if my afternoon was well spent today.

Atsunori

That afternoon was very well spent! I learned that something other than X10 was supported, which I didn't realize, and those numbers are very interesting!

[...]

Also see e.g.

--

John Devereux

Atsunori Tamagawa schrieb:

Thanks a lot for what you found out. I'll try to do the same for another scope and report what I find here.

Does anyone know where one can get BNC connectors with the outer metal ring that connects to the probe pin? Maybe it's easier to just use a normal connector and add the ring myself though.

Philipp

John Devereux schrieb:

There's lots of probe interfaces mentioned there. However AFAIK only Plain BNC and what they call "TekProbe-BNC Level 1" are some kind of industry standard. The rest seem to be Tektronix proprietary.

Philipp

Thanks for your inspiration on how to spend a nice afternoon! Here's the results (not that much, the equipment is old, most of the stuff doesn't have readout pins):

Probe Type Readout R

---------- ---- --------- TEK P6111B x10 11k4 TEK P6114B x10 11k1

Readout R TDS360

--------- ------

20k x1 16k x1 15k x10 13k x10 12k x10 11k x10 8k2 x10 7k5 x10 6k8 x100 5k6 x100 4k7 x100 3k6 x1 3k x1 2k7 x10 2k4 x2 2K2 x2 2K x5 1k8 x5 1k6 x20 1k5 x10 1k3 x20 1k2 x50 1k1 x50 1k x200 820 x200 750 x500 680 x500 620 x500 560 x1000 470 x1000 360 x1000 300 x1 100 x1 10 x1

Looks like they started using whatever resistor they had (2k7, 1k5) to mark x10 probes and later came up with a more generic scheme, but had to leave some intermediate values at x10 for backwards compability.

Philipp

Atsunori Tamagawa schrieb:

Is this the same as Agilent Autoprobe?

Philipp

8/06/2009 ?., 15:36:19 UTC+3 PeterD :

Because this low-impedance probe and its divider are formed with an input i mpedance of an oscilloscope of 50 ohms. And when you turn on the input of a n oscilloscope of 1 M?, you do not have a division by 10.