Quadchek II 7564SA - Electrical Safety Compliance Analyzer

I bought this the other year on Ebay for a ridiculously cheap amount of money, but I didn't manage to get any output from it when I tried it,  so - I thought I'd take another look;  after a bit of googling I found out the unit required an interlock fitted to the back to enable the outputs to work;  not sure if this was retro-fitted sometime later as a safety feature? idk,  anyway, it turned out you can defeat this by simply shorting pins 4 & 5 on the input port;  so,  after doing this, the unit seemed to work perfectly;  the only issue was I don't have any the correct chunky HV test leads, so,  I had to rig some quick and dirty leads up to it in order to test it.

Below are 3 pics showing the testing of a 68V bi-directional TVS Diode.

Below is a pic showing a low ground bond test current being measured on my DMM.

Below are a few tear-down pics I took last year.

Cropico ESC1 Electronic Standard Cell

A few days ago I managed to buy one of these for £5.50 on Ebay, it was was one the first zener diode replacements for the Weston cell,  but when I powered it up from my bench power supply it was dead!   so,  I cracked it open and after a while checking through the components I discovered one of the tantalum caps had shorted,  so I replaced that with an electrolytic one of the same value and when I powered-it-up,  it was working once again!.

The bad cap which was replaced!














The unit powers-up with 27 volts (or 18 x 1.5 volt C cells! ) and consumes ~16mA

From some measurements I took with my 7150 it seems that my 7150 has drifted quite a bit from the cal I had done a few years back;   the good thing is I can reasonable confirm this drift because the 1.0000v reference from my Time 2003S reads exactly the same on the 7150 as the Standard Cell.

The 7150 readings were..

Standard Cell  @ 1 volt
0.999815 volts

Time 2003S @ 1 volt
0.999815 volts

IDM305 DMM 1
0.9989 volts

IDM305 DMM2
0.9986 volts

Ambient was approx ~19.5 degrees C.



Inside the cover of the unit was a historic record of the measured Standard Cell voltages.

An identical unit was taken apart over on one of the popular electronics forums eevblog, the linked page also contains some useful PDFs.

http://www.eevblog.com/forum/metrology/cropico-esc1-electronic-standard-cell-a-look-inside/


This is another useful link to a site called "Johns Virtual Museum of Interesting Gadgets" where gives a short bit of information about the unit.

https://sites.google.com/site/johnhurll/home/cropico/ecs1-electronic-standard-cell

TENMA 72-10495 2CH 0-30V 5A Power Supply

This is my new power supply,  I was tried of using my old one which was a complete pain to use as the voltage and current adjustment was far too course;  this TENMA one has a digital pot which allows for course and fine adjustment.  Initially when it arrived I let it warm up to ambient room temperature before I switched it on;  then I tested both channels with both light and moderate loads and it all seems to work really nice;  the fan speed is variable based on the load,  and when you turn the pot through the entire voltage range you can hear it using relays to switch through the various transformer taps.

A few weeks later...

Well now I've had chance to play around with it a bit I must say it's really quite nice.  my only niggle with the unit is in the way that when you set either a voltage or current directly it always defaults to voltage and always at the volt unit,  this is a pain if you need to periodically tweak the millivolt, say if you were simulating a 0 - 5 volt sensor.  the other niggle is you can only change the voltage and current while in edit mode,  and after a few seconds it auto exits edit mode;  and entering edit mode always takes you to voltage and the volt unit and not the last unit (millivolt) setting.

I haven't tested the power-on voltage curve under max current conditions as I don't have a dummy load, but I'm guessing there wouldn't be much overshoot to worry about.

GM Tubes

Some GM Tubes for a project I plan to build some time next year.

A Posse of Transformers

Nice little Ebay snip;  30 transformers for £12 - perfect for my kiln controller boards  ;-)

DC Voltage Calibrator

This is something I bought from Ebay for £30.  It can output a voltage between 0.01uV to 9.9999v @30mA,   It contains a precision zener diode which is used as a reference input to a FET chopper amplifier operating in feedback stabilized mode.  The gain is determined by a set of precision metal film resistors which are selected by the 5 decade thumbwheel.

Looks like it was circa 1987.

The battery pack consists of 11 x 1.2 Volt AA Ni-Cads @ 700mA.  They were assembled in 1998 and they starting to leak.

Because I didn't want to go to the trouble and expense to replace the batteries, so I just removed them from the unit instead.

Experiment - Simulating VR Signals

Over the last couple nights i've been looking at creating some simulated variable reluctance sensor signals.

The scope picture above shows the finished crank and phase signal waveforms being output from the bread-board circuit into channel 1 & 2 of the oscilloscope.

Although I was quite pleased with the results it would be nice to develop the project a little more perhaps when I have more time to do so.

The circuit consisted of a small PIC uC that outputs the desired shaped waveform into a 6 bit resistor ladder DAC;   then the DC signal was fed into a single operational amplifier which negatively offsets the DC signal to create a nice AC signal;  after that the signal is simply multiplexed to create both the crank and phase.





Once I had increased the total number of sample points in my waveform the shape started to look much better.

As you can see I used quite a lot of trimmer POTs;  I couldn't find any 2R values in my parts box, so instead of using two-of  the same value Rs,  I just used some cheap POTs I had.

Overall the circuit worked well.