See my comments just after your points...
On Thu, May 10, 2018 at 03:46 pm, Mike Merigliano wrote:
Hello Fabio,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 forThe 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.