Test and
Measurement Design
T&M and Process Control Instrumentation have many things in common;
but the conditions in which a Industrial Instrument works, may be very
unfriendly.
Industrial Instruments are used both in Clean-Cool Control Rooms and
also in a corrosive, humid, hot and vibrating industrial environment.
Even high
levels of Static, Magnetic influences in conjunction with spikes and
brown outs can be expected.
Test and Measurement instruments are of two types, by way of
its usage; Portable and Benchtop. Portable Instruments will consume
low power, insulated and rugged. The Product Safety features are more
stringent as they are HandHeld or slung over the shoulder. Some
features and specs are sacrificed. The Benchtop version has more
front panel space and can interface with other instruments or systems.
More accuracy and features can be accommodated in this.
This was a Beta Hfe and Vce Measuring Instrument used in Incoming
Inspection of Power Transistors made by me 16 years back.
Instrumentation Notes -
- If the waveform on the scope droops then you
may need to use a 10X attenuating probe or mode. this attenuator is at
the tip of the probe hence better measurement possible, also very high
frequency signals may be best transmitted over a 50 ohm impedance
matched line to the Oscilloscope.
The History
of Oscilloscope, Learn more about Oscilloscope from the Innovator
of the Scope as a Measuring Instrument here is XYZs of
Oscilloscopes.
- Karl
Ferdinand Braun - In 1897 he built the first cathode-ray
tube...oscilloscope. CRT technology is to this day used by most
television sets and computer monitors. The CRT is still called the
"Braun tube".
- Test a NPN transistor, DMM in 200K range.
emitter negative probe, collector positive probe, it should show open.
while still holding that way press wet finger on base and collector, it
may show some reading, then it is ok. for PNP swap probes polarity and
do the same thing. the wet finger when pressed applies a base current
in uA.
- Testing a
Mosfet - Transistor
Tester - Basic
Testing of Semiconductor Devices
- The most common reason of DMM failure is when a
person tries to measure 230V AC with a DMM in current or ohms mode,
with the probes in the wrong sockets. Use external attenuators and
shunts.
- A DMM in diode mode or resistance mode can be
used to test IR diodes, take it under 100W lamp and measure, cover the
IR diode and measure you will see a response in proper polarity.
- If you put the DMM in 2V mode and measure the
voltage across a ordinary LED near a 40W lamp you will see around
200mV. Turn off 40W lamp the mV will fall near 0. Even metal-can
transistors with their top ground away will become photo sensors.
- When you measure low voltages or high
resistance like 1M with a DMM your body must not be in contact with the
probe tips. Body resistance is low in comparison so error in reading or
loading of mV from sensor, in sensitive and high impedance ranges.
- Do not use an oscilloscope to measure 230V
directly, use a transformer, differential probe or attenuator.
- An oscilloscope 1M probe or a DMM 10M impedance
can load circuits with nano-pico amps of bias.
- Red socket and probe for positive and black
socket and probe for negative
- Is it oscillating ?.... We cannot say, it could
also be DC, you need to see if a Clock is present. use a signal tracer
or a DMM freq mode, or AC measurement. or build this solorb.com-elect-logicprobe.
When you do not have a scope you can build one for the PC.
- Polarity and Zero Cross, a polarity indicator,
which will tell you to
swap the leads.Zero
Crossing
Detectors, Comparators,
Discover
Circuits - Zero Cross.
Related Resources
13:08 17-Jul-09
Anantha Narayan
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