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Discussion of precise voltage measurement

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Cal labs

Joseph Gray

Mon, Jul 29, 2013 12:44 AM

Has anyone used either of these companies? What is your opinion?

For a 3478A, Techmaster lists the following prices:

ISO 9001 = $50
Z540 = $175
ISO 17025 = $275

Now, I realize that these are various standards. Without me having to read
reams of standards documents, can someone tell me briefly what the
difference is and which of these do I need as a hobbyist and potential volt
nut? Also, they have a column heading of "Level" and for the 3478A, it
lists level 4. What does this mean?

They also list the EDC MV106, starting at $100. I'll have to contact them
about the EDC VS330.

Boy, just what I needed. Another hobby that costs money :-)

Joe Gray
W5JG

I found that there are at least two cal labs in El Paso, which is reasonably close to me. One, Techmaster Electronics has pricing listed (I hate it when everyone says "contact us for a quote"). The other is MetroCal, which lists no information at all. Has anyone used either of these companies? What is your opinion? For a 3478A, Techmaster lists the following prices: ISO 9001 = $50 Z540 = $175 ISO 17025 = $275 Now, I realize that these are various standards. Without me having to read reams of standards documents, can someone tell me briefly what the difference is and which of these do I need as a hobbyist and potential volt nut? Also, they have a column heading of "Level" and for the 3478A, it lists level 4. What does this mean? They also list the EDC MV106, starting at $100. I'll have to contact them about the EDC VS330. Boy, just what I needed. Another hobby that costs money :-) Joe Gray W5JG

David Kirkby

Mon, Jul 29, 2013 6:35 AM

On 29 July 2013 01:44, Joseph Gray jgray@zianet.com wrote:

Has anyone used either of these companies? What is your opinion?

Like you, I am not keen on the "POA".

I have never had any voltage things calibrated myself - my HP 3457A
has not been caibrated for a decade or so.

But I do have some of my RF things calibrated by Techmaster
Electronics, as they were calibrated by them when I purchased them.
One is a HP 8720D vector network analyzer and the other is a Agilent
85033E 3.5 mm calibration kit, which is used to calibrate the VNA.
There are several things that make me very suspicious of Techmaster
Electronics.

Agilent state the equipment to verify the performance of the 85033E
VNA calibration kit is not commerically available, so one has to
question how anyone else other than Agilent can do it. (In practice, I
suspect it gets returned to Maury Microwave, who make it for Agilent).

The 85033E's cal certificate lists what Techmaster Electronics used
for the 9 GHz 3.5 mm cal kit, and I'm not impressed at all. They used
a 6 GHz type N calibration kit, an HP 8510 VNA and a simulation
package. It fairly clear to me that such a list of equipment is not
able to properly determine if a 9 GHz 3.5 mm calibration kit is within
the specs set by Agilent.

I think one could get a reasonable degree of confidence in a VNA cal
kit using a good VNA, the calibration kit and a verification kit.
But that is certainly not a real calibration. I suspect the only way
to really verify the performance would be using things like laser
micrometers to make mechanical measurements of the standards - not
electrcal measurements on a VNA.

My VNA was calibrated by Techmaster Electronics too. I note the
calibration certificate says under the notes that optoin 010 was
added. Now option 010 is a software option to enable the TDR
functionality of the VNA. There are known hacks to add this, and a cal
lab might well have other ways to add it, by entereing a software
code. But I doubt option 010 was legally added, since the VNA is
unsupported by Agilent and the option can't be bought.

So basically my confidence in Techmaster Electronics is zero. I
question their ability to calibrate things they issue cal certificates
for, and I question their integrety.

My HP VNA is due for cal now. It expired a few days ago and I have
contacted Agilent to get it calibrated - I would personally not trust
any other lab. That's not to say there are not other labs capable of
calibrating an HP VNA, but there is not one I would trust.

I would say a 5.5 digit DVM is probably easier to cal than a VNA or
VNA calibration kit, so the fact I'believe Techmaster Electronics are
issuing cal certificates for things they can't calibrate, it would not
surprise me if they could do a decent job on a 5.5 digit DVM. Agilent
will charge you $200 to do the DVM. Personally I'd pay the $200 and
get them to do it, but its easy to say that when I'm not paying!

As for what the different cals mean, I know in the case of Agilent
VNAs, irrespective of what cal you order, the cal will use the same
equipment, so you end up with the instrument working the same. What
changes is whether you get documented uncertainties, guard bands, and
in some cals one gets a report of its performance before calibration
as well as after calibration. For me personally, the cheapest cal from
Agilent is good enough, as I don't need the extra information and so
don't want to pay a lot to get it.

Dave, G8WRB

On 29 July 2013 01:44, Joseph Gray <jgray@zianet.com> wrote: > I found that there are at least two cal labs in El Paso, which is > reasonably close to me. One, Techmaster Electronics has pricing listed (I > hate it when everyone says "contact us for a quote"). The other is > MetroCal, which lists no information at all. > > Has anyone used either of these companies? What is your opinion? Like you, I am not keen on the "POA". I have never had any voltage things calibrated myself - my HP 3457A has not been caibrated for a decade or so. But I do have some of my RF things calibrated by Techmaster Electronics, as they were calibrated by them when I purchased them. One is a HP 8720D vector network analyzer and the other is a Agilent 85033E 3.5 mm calibration kit, which is used to calibrate the VNA. There are several things that make me very suspicious of Techmaster Electronics. 1) Agilent state the equipment to verify the performance of the 85033E VNA calibration kit is not commerically available, so one has to question how anyone else other than Agilent can do it. (In practice, I suspect it gets returned to Maury Microwave, who make it for Agilent). The 85033E's cal certificate lists what Techmaster Electronics used for the 9 GHz 3.5 mm cal kit, and I'm not impressed at all. They used a 6 GHz type N calibration kit, an HP 8510 VNA and a simulation package. It fairly clear to me that such a list of equipment is not able to properly determine if a 9 GHz 3.5 mm calibration kit is within the specs set by Agilent. I think one could get a reasonable degree of confidence in a VNA cal kit using a good VNA, the calibration kit and a *verification* kit. But that is certainly not a real calibration. I suspect the only way to really verify the performance would be using things like laser micrometers to make mechanical measurements of the standards - not electrcal measurements on a VNA. 2) My VNA was calibrated by Techmaster Electronics too. I note the calibration certificate says under the notes that optoin 010 was added. Now option 010 is a software option to enable the TDR functionality of the VNA. There are known hacks to add this, and a cal lab might well have other ways to add it, by entereing a software code. But I doubt option 010 was legally added, since the VNA is unsupported by Agilent and the option can't be bought. So basically my confidence in Techmaster Electronics is zero. I question their ability to calibrate things they issue cal certificates for, and I question their integrety. My HP VNA is due for cal now. It expired a few days ago and I have contacted Agilent to get it calibrated - I would personally not trust any other lab. That's not to say there are not other labs capable of calibrating an HP VNA, but there is not one I would trust. I would say a 5.5 digit DVM is probably easier to cal than a VNA or VNA calibration kit, so the fact I'believe Techmaster Electronics are issuing cal certificates for things they can't calibrate, it would not surprise me if they could do a decent job on a 5.5 digit DVM. Agilent will charge you $200 to do the DVM. Personally I'd pay the $200 and get them to do it, but its easy to say that when I'm not paying! As for what the different cals mean, I know in the case of Agilent VNAs, irrespective of what cal you order, the cal will use the same equipment, so you end up with the instrument working the same. What changes is whether you get documented uncertainties, guard bands, and in some cals one gets a report of its performance before calibration as well as after calibration. For me personally, the cheapest cal from Agilent is good enough, as I don't need the extra information and so don't want to pay a lot to get it. Dave, G8WRB