Calibration Of Electronic Equipment In The Home Workshop

[Too_Many_Tools]

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?

Links to recommended circuits, pictures and sources would be
appreciated.

Since this is a need for anyone who has test equipment, I hope to see
a good discussion on this subject.

Thanks

TMT

 

[chuck]

It depends entirely on what you need the equipment for.

If for any legal reason you need NBS traceability, then the question
of how and how often is already answered by your regulatory agencies.

If you don't, then I cannot imagine that a couple off-the-shelf
precision resistors, voltage references, and frequency references
(total cost: $10) would not be good enough for sanity checking for
almost any pedestrian uses.

If you're the sort who keeps equipment on your bench just to calibrate
equipment on your bench just to calibrate equipment on your bench,
then any rational argument about traceability is pointless because
you've already set yourself up in an infinite circular loop.

Tim.

A lot of good points have been made already so I'll just add a small one.

Don't mess with calibration of quality equipment unless you have reason
to believe the calibration is off AND THAT IS ADVERSELY AFFECTING YOUR
WORK PRODUCTS. An amazing amount of electronics work has been done using
equipment with non-current calibration stickers, some of which was out
of calibration.

If metrology is something that interests you as a hobby, then jump into
it and have fun. Tim's last paragraph ought to be printed and framed.

Chuck

 

[MassiveProng]

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?

Links to recommended circuits, pictures and sources would be
appreciated.

Since this is a need for anyone who has test equipment, I hope to see
a good discussion on this subject.

If you have used test gear, and you do not intend to PAY to have it
calibrated, you be best off leaving it all the **** ALONE!

 

[James Sweet]

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?

Links to recommended circuits, pictures and sources would be
appreciated.

Since this is a need for anyone who has test equipment, I hope to see
a good discussion on this subject.

Thanks

TMT

What sort of equipment are you trying to calibrate? You can do a search
online for various voltage reference sources. Accurate frequency
reference can be picked up off the airwaves from transmitters such as
WWV. What methods you use depend on what the equipment is and how
accurate you need it to be.

 

[[email protected]]

If you have used test gear, and you do not intend to PAY to have it
calibrated, you be best off leaving it all the **** ALONE!

As alone as you on a Friday night?

 

[Jim Yanik]

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?

Links to recommended circuits, pictures and sources would be
appreciated.

Since this is a need for anyone who has test equipment, I hope to see
a good discussion on this subject.

Thanks

TMT

Wavetek and Fluke both make nice all-in-one calibrators for voltmeters and
scopes,they do V,I,R,timing and bandwidth checks.Not cheap,though.
There's plenty of older,used cal standards on the market,too.
Getting them certified may be a problem due to their age.

For F-counters,you need a WWV or GPS-based receiver.

high-end stuff,you send out to a lab.
(consider them your "primary standards")

A warning;calibration procedures of some TEK gear may be written to use
their recommended list of standards,and difficult or impossible to do fully
with substitutes.
Especially their video test gear.

 

[Ken Smith]

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?

For frequency, you can use WWV. You need:
A short wave radio with an audio output.
Perhaps an audio filter tuned to about 1KHz.
A generator you wish to calibrate near the WWV frequency.
A frequency counter that is not too far off.

Procedure:
Tune in WWV.
Put wire on generator and set it to WWV-1KHz
Listen for tone and move stuff around until it sounds good.
Feed tone into the filter.
Place the counter on the output of the filter.

The number on the counter is X Hz away from 1KHz when the generator is XHz
off from WWV-1KHz.

 

[Phil Allison]

** Groper alert !

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?

** A few 0.1% precision resistors does the first job for DMMs.

A Natsemi " LH0070 " 10.000 volt ( +/- 0.02% ) voltage reference IC with
0.1 % resistor divider chain giving 1.000 & 0.1000 volts for the DC volts
ranges DMMs and scopes does the second.

For AC volts, a scope screen with internal graticule is used to establish
the p-p amplitude of a sine wave - then it can be used to check then AC
ranges DMMs etc - to a 1% accuracy.

A 12MHz crystal oscillator ( 11.99993 MHz @ 25C ) checks the DFM -
calibrated using an off air standard frequency transmission picked up on a
scanner.



........ Phil

 

[David L. Jones]

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?

Links to recommended circuits, pictures and sources would be
appreciated.

Since this is a need for anyone who has test equipment, I hope to see
a good discussion on this subject.

If you've got that sort of gear at home then usually you have better
(and calibrated) gear at work as well, in which case most of us would
simply bring in our gear from home and spot check it against the good
gear.

In the absense of this gear, you can simply use precision components.
Voltage reference chips with 0.05% or better are cheap and readilly
available.
0.01% resistors are available too.

If you have multiple meters for example, you can also keep an eye on
them by comparison. Using any old component, if all three meters read
the same then you can be pretty confident they haven't drifted.

Checking scope horizontal timebases is easy with a crystal oscillator
and divider.

There are various methods for getting an accurate frequency standard,
but one of the newst methods is using a GPS derived reference. Second
hand Rubidium standards can also be had on eBay.

Generally though, good quality test gear does not drift out of spec,
so the need for regular calibration is minimal.

Dave

 

[Too_Many_Tools]

If you have used test gear, and you do not intend to PAY to have it
calibrated, you be best off leaving it all the **** ALONE!

LOL

You're a real ray of sunshine, aren't you?

Now go out and play in traffic while we adults talk about serious
stuff..

TMT

 

[Too_Many_Tools]

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?

Links to recommended circuits, pictures and sources would be
appreciated.

Since this is a need for anyone who has test equipment, I hope to see
a good discussion on this subject.

Thanks

TMT

Thanks for the (positive) comments so far.

I look forward to any more you might want to offer.

Any circuits or examples others have done?

Any cal boxes that anyone have built?

TMT

 

[Robert Baer]

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?

Links to recommended circuits, pictures and sources would be
appreciated.

Since this is a need for anyone who has test equipment, I hope to see
a good discussion on this subject.

Thanks

TMT

You left many things unsaid: (a) Traceable to NBS/NTIS or not; (b) if
not, how many reliable digits; (c) at what cost.
You can make a 5V "standard" that any loading will not damage with
error better than 0.5mV and runs for at least 6 months with no
observable change - and the cost is only a few dollars (uses
off-the-shelf parts).
You can buy thru DigiKey, resistors rated at 0.05% and at 0.1% -
rather decent as references.
You can buy a Fluke bench meter rated at 6.5 digits and even pay a
bit more for traceability.

 

[Robert Baer]

If you've got that sort of gear at home then usually you have better
(and calibrated) gear at work as well, in which case most of us would
simply bring in our gear from home and spot check it against the good
gear.

In the absense of this gear, you can simply use precision components.
Voltage reference chips with 0.05% or better are cheap and readilly
available.
0.01% resistors are available too.

If you have multiple meters for example, you can also keep an eye on
them by comparison. Using any old component, if all three meters read
the same then you can be pretty confident they haven't drifted.

Checking scope horizontal timebases is easy with a crystal oscillator
and divider.

There are various methods for getting an accurate frequency standard,
but one of the newst methods is using a GPS derived reference. Second
hand Rubidium standards can also be had on eBay.

Generally though, good quality test gear does not drift out of spec,
so the need for regular calibration is minimal.

Dave

True, 0.01% resistors are available, *but* they are extremely
expensive (over $100 each) and they are made when and if the
manufacturer sees fit to do so.

 

[Homer J Simpson]

I look forward to any more you might want to offer.

If it was me, I would start by reading Scroggie's Radio Laboratory Handbook.

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[Glenn Gundlach]

LOL

You're a real ray of sunshine, aren't you?

Now go out and play in traffic while we adults talk about serious
stuff..

TMT

I agree with Prong on this one. I've worked in repair and broadcast
for 35 years. Unless you have a compelling reason to change it, leave
it alone. Of course, this assumes it's good stuff to begin with like
Fluke and Tek.

The only time I altered a Fluke 8060 was an eBay purchase. When
testing some new boards, I was reading 4.998 on the 5 volt ref. Never
saw any boards that far off and then tried the other Fluke which was
as expected. The eBay meter got a little 'tweak' but that was very
unusual. BTW, the 5V ref on the boards was an ADI AD588 which is
almost good enough for the 8060. I would use it to cal a 3.5 digit
meter with no qualms.

GG

 

[David L. Jones]

True, 0.01% resistors are available, *but* they are extremely
expensive (over $100 each) and they are made when and if the
manufacturer sees fit to do so.

Not so.
RS Components have 0.01% resistors for AU$34.50 (US$26)
Farnell have 0.02% for as little as AU$20

Dave

 

[Dr. Anton T. Squeegee]

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

<snippety>

I could post pictures... ;-)

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?

Hmm. Excellent question.

For frequency, I actually have three different references, all GPS-
locked. One is my primary reference, an HP Z3801, as retired from a
cellphone site. The second and third ones are both combination clocks
and freq-references, one from Trak Systems (now Trak Microwave) and the
other from Odetics/Zypher. All three use a very stable OCXO that is
constantly disciplined by the GPS receiver.

Long-term accuracy is on the order of 1E10 -11th or so. In other
words, about as good as you can get without being NIST certified.

I don't have good primary voltage or current references as yet.
That's on the 'Acquire' list for scrounging this year. For resistance,
simple Pomona plugs with 0.01% tolerance resistors work pretty well for
2-wire. For anything more, I will probably have to rent one of the Fluke
all-in-ones.

I'm just beginning to gather the goodies I need for calibrating my
O-scope collection. That will eventually consist of Tektronix leveled
sine-wave generators, and one of their CG5xxx series calibration
generators.

Keep the peace(es).

 

[doug]

For frequency, you can use WWV. You need:
A short wave radio with an audio output.
Perhaps an audio filter tuned to about 1KHz.
A generator you wish to calibrate near the WWV frequency.
A frequency counter that is not too far off.

Procedure:
Tune in WWV.
Put wire on generator and set it to WWV-1KHz
Listen for tone and move stuff around until it sounds good.
Feed tone into the filter.
Place the counter on the output of the filter.

The number on the counter is X Hz away from 1KHz when the generator is XHz
off from WWV-1KHz.

This works if you only need about 1 part in a million. The movement of
the ionosphere makes wwv useless for real calibration. This was, of
course, wonderful when we had nothing else. It is far better to get
a gps standard (they are used on cell sites and show up on ebay) and
just use it for the timebase all the time. Alternately, use a Rb
source. They were also used in cell sites and are available easily.
They cannot move more than about a part in 100 million and they make
excellent time bases for frequency counters.

 

[JW]

[...]

True, 0.01% resistors are available, *but* they are extremely
expensive (over $100 each) and they are made when and if the
manufacturer sees fit to do so.

Not so.
RS Components have 0.01% resistors for AU$34.50 (US$26)
Farnell have 0.02% for as little as AU$20

You guys are paying *way* too much. We use Riedon .01% precision resistors
in our A/D products, and pay about 5 bucks apiece. Their site is down at
the moment, but even Digikey has .01% resistors for around the same price:
http://www.digikey.com/scripts/DkSearch/dksus.dll?Criteria?Ref=3107&Site=US&Cat=34342147

 

[JW]

I look forward to any more you might want to offer.

Any circuits or examples others have done?

For a cheap voltage reference, I would look into Analog device's AD780
series. The AD780BN has an initial error of +-1mV and is available in a
plastic 8 pin DIP for easy assembly. Download the data sheet and you'll
find sample circuit diagrams. Be sure to use a nice clean power supply and
use good decoupling practices around the device.

For resistance, see my post with a link to Digikey.