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Tuesday, December 09, 2014

Digital Insulation Tester

This is a photograph of a 20 Tera Ohm Insulation Tester I made around 20 Years Back. It had even Polarization Index for Transformer Insulation.

Digital Insulation Tester

The Product above is made with two circuits below.
A regulated, low ripple, high voltage of very low current capability is applied by instrument on a DUT (device under test). The leakage current in nA or pA (picoamps, nanoamps) is measured and readout, The Innovation i did was to measure the current in Vref and not Vin of ICL7107, this made the 1/x computation.

Insulation Tester or Tera Ohm Meter with Polarization Index

Also using the ICL7650 Chopper Stabilized amplifier must be done as shown in data sheets with grounded guard rings. pA will leak on the PCB itself if layout is not done keeping this in mind.

Sunday, December 07, 2014

DMM or Digital Multi Meter

A nice DMM is the first thing you should own. Have one for High Voltage and High Energy and another for Workbench Testing.

DMM or Digital Multi Meter

Better to use external attenuators and shunts when high energy is involved. Make yourself and your instruments last for some time. Safety is first. Footwear and Gloves can help.

Tutorials on Basics and Instrumentation Electronics

Digital Multi Meter - New Year Resolutions
  1. I will not drop the DMM from a height of 4 feet.
  2. I will not Test Live Powered equipment in the Ohms Mode.
  3. I shall not Measure Mains Voltage in The Current Mode.
  4. I shall get it calibrated once a year or at least once a decade.
  5. I shall not use it in High Energy Measurements.
  6. I will try my best not to give it to my best friend.
  7. I can remember Red is Positive and Black is negative.
  8. I will wear shoes and stand on a block of wood while i test.
  9. I shall not operate the rotary range switch at high speeds.
  10. I shall replace the probes-cables-connectors on wear-tear.
  11. I shall not accidentally keep the hot-iron near the DMM or leads.
  12. I shall not keep DMM on tall table and pull it with the leads.

Thursday, December 04, 2014

Transformers Series and Parallel Connections.

Series and Parallel Transformers

Series and Parallel Connections in transformers. Observe the Dot-Polarity. When windings are in parallel the current capacity doubles. When windings are in series the voltage doubles. Wrong dot polarity in series connection just cancels the voltage and a small residual imbalance voltage remains. If wrong polarity connection is done in parallel, then a short circuit or overload may occur.

Basic Electrical Circuits

Series and Parallel Transformers
Center Tap Transformer

This is when you need to build a symmetrical dual supply like +12V and -12V supply for an opamp design.
This is also good for a two diode full wave rectifier. But when you make a dual supply use a bridge and the center tap is ground. If you use just two diodes then one winding may be loaded more than other. That may not be good for long term transformer life. The core may get magnetized.

Center Tap Transformer