Re: 453 calibrator

Fabio Trevisan

Hello Mike,

See my comments just after your points...

On Thu, May 10, 2018 at 03:46 pm, Mike Merigliano wrote:
Hello Fabio,
The 1 volt output is at the BNC (J579), so the 200 ohms are not included
and I get 1 volt peak-to peak here at the 1 volt setting, and 0.1 at the
0.1 setting (with another 180 ohms).
Either I don't understand what you mean by "so the 200 ohms are not included" or you didn't realize that R1274 (2k19), R1275 (180R) and R1276//R1277 (20R) together, form a voltage divider with 2 output "taps" or yet, you don't know what a voltage divider is and how it works.
I will assume the first.
The switch only selects which tap of the output divider is actually being routed to the output.

Anyway, I figured it out... The design of the calibrator voltage divider is indeed lacking, so to speak, but it's compensated by the calibration instructions of the +12V power supply.
The calibration of the +12V power supply is made aiming at getting the right output voltage from the calibrator, and not aiming at a "spot-on" +12V voltage.
Quoting the service manual:
"Adjust +12-Volt Power Supply (R1152) Page 5-8 REQUIREMENT: +1 volt, +-0.01 volt, at 1kHz CAL connector with Q1255 removed. +12.1 volts, +- 0.2 volt output from supply"
So you can see that the +12V power supply is not really expected to be at exact 12V, but rather centered around 12.1V.

The probe loop on the 453 is for
calibrating a current probe. I do not see a 1kHz signal on the current
probe using a passive 1x probe (Tek P6028), just a lot of noise at mixed
frequencies at around 5 mV p-p.
The Tek P6028 probe you mentioned is not a current probe, it's a x1 voltage probe and it can't measure current (unless you break the circuit and insert a small resistance in series, and measure the voltage drop across the resistor).
A current probe is a magnetically coupled device, that senses the magnetic field induced by the current flowing through a wire, that you hook the current probe's magnetic core around it (like a Clamp current meter, but usually smaller).
There are current probes that uses a coil around the magnetic core, and therefore can only sense AC current, and there are ones that uses hall-effect transistors to sense the magnetic field, which can sense DC current but is limited in frequency to the hall transistor's frequency response.
I never got my hands on either, and I suppose the more advanced ones possibly uses the hall transistor for DC up to some frequency, and a coil for all frequencies above that, and mix the outputs in order to provide a wide band current sensing, from DC up to whatever is the probe's bandwidth, but I don't really know.



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