Test Equipment Anonymous (TEA) group therapy thread

[Specmaster]

Cheap HV probe on ebay this morning. 26$

https://www.ebay.com/itm/BECKMAN-INDUSTRIAL-HV231-22-HIGH-VOLTAGE-PROBE/274689423954

I don't like the hook on the end. When measuring HV my mantra is get on and get off ASAP. With that hook you could easily get hung up. 

My thoughts precisely.

[capt bullshot]

That's a real beast: 4x 1000V / 30A   
A Yokogawa WT3000 Precision Power Analyzer, complete with 4 modules.

Nice one, but a bit above my budget
BTW, this seller has a Agilent E3631A for 450EUR.

For 3ph power measurements, I've got this one:


It's a special version of an instrument I developed at a former job (only this particular one was built as a special version). I cannot do it's intended function (measure the power line impedance over frequency 3Hz ... 20kHz), but has all the other functions like power meter, harmonics, flicker, ... As it doesn't have an UI, one needs an old W95 laptop to run the original software. For this reason, I rarely use it.

[Specmaster]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

[capt bullshot]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

You can tell them apart by the reduced or missing dielectric, like this random 75 Ohm BNC Tee.

[mansaxel]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

The quick version is that a 50Ω has more dielectric in the male plug, where the 75Ω is just air.

Also, there's a thread on this forum discussing it. I mean: Apparently, there are other threads on this forum... 

[BU508A]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

The quick version is that a 50Ω has more dielectric in the male plug, where the 75Ω is just air.

Also, there's a thread on this forum discussing it. I mean: Apparently, there are other threads on this forum... 

"Jetzt, wo du es sagst, sehe ich es auch."   

[Cerebus]

I got to the same point in my line of thought on the matter. Then I decided I’d just buy a load. Then I decided I didn’t need one enough to buy one. So now I have some power resistors and a calculator and make do. This quickly evolved into “stop buying things you need a load for” 

I can live without a proper electronic load and have done so; my thinking around acquisition hasn't been too far from yours. The two things that drive me in wanting one actually both involve making the same measurement, namely measuring PSU recovery from a step/pulsed load change. Every time I get a new PSU and run through the verification routine in the manuals I feel a bit shabby that I skip the step that verifies regulation, excursion and settling time from a step load change. I also have a long standing 'to   do   complete' which is to design and build some really pukka linear bench PSUs - I'll need to make the same measurements in verifying/refining my designs for these.

Start there, and then add the thinking "While I'm at it, I ought to do a proper job and add constant resistance for battery testing. Oh, and if I'm going to bother with that, I ought to do constant power too.". This may be an example of the best being the enemy of the good.

[mnementh]

Re: Electronic Loads

As "good" and "reasonable price tag" ones appear to be quite rare at the usual sources, and for a project I needed one with CC / CV / CP modes that can do more power than the HP6632B, I bought a cheap one two months ago: The Kunkin KP184 - 400W in a quite small box. Nothing fancy, not a reputable brand, totally misplaced between all the Toellner, Heinzinger, Oltronix, HPAK etc power supplies, but it does the job.

https://www.banggood.com/search/electronic-load.html

Hmmmmm...   It has been a long time since I checked them out for this particular type of tool; it appears bang-em-good has upped their game with a fair selection of budget electronic loads for almost any application along with the KP184, including these which appear to be a cousin using a nice color LCD (but obviously, not necessarily better quality or capability):

   

https://www.banggood.com/ET5410-Professional-DC-Electronic-Load-Programmable-Digital-Control-Battery-Capacity-Tester-Electronic-Loads-400W-150V-40A-p-1613467.html

https://www.banggood.com/RS232-DCL6204-Communication-Double-Channel-Programmable-DC-Electronic-Load-with-150V-20+2A-400W-Battery-Tester-p-1620007.html


And they even have a few which are attractive for the "coathangers & baling wire" & "I can't be arsed to hack it together myself" budgets:

      

https://www.banggood.com/Original-ZHIYU-60W-or-110W-9_99A-30V-Constant-Current-Electronic-Load-Aging-Battery-Capacity-Tester-p-1146280.html

https://www.banggood.com/150V-10A-150W-LCD-Digital-Adjustable-Constant-Current-Electronic-Load-Battery-Tester-Lithium-Discharge-Capacity-Voltage-Meter-p-1662009.html

https://www.banggood.com/250W-DC-12V-Discharge-Battery-Capacity-Tester-Module-With-DC-Electronic-Load-Digital-Battery-Tester-p-1383823.html

These cost from $30-60 delivered to me in the GWN, and many of them have exactly the kind of battery cell-health/capacity characterization features I've been wishing for or making do with my PSU & aging Power Analyzer; even on some of the cheaper ones. Even these cheapies are far superior to anything I could knock together from those modules without for days, with a BOM that would doubtlessly be more than their delivered price by the time I was done, especially if I had to buy a fan/heatsinks. 

EDIT: Attached manual for KP184

mnem
 

[Specmaster]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

The quick version is that a 50Ω has more dielectric in the male plug, where the 75Ω is just air.

Also, there's a thread on this forum discussing it. I mean: Apparently, there are other threads on this forum... 

"Jetzt, wo du es sagst, sehe ich es auch."   

No need to be shy 

[bd139]

I got to the same point in my line of thought on the matter. Then I decided I’d just buy a load. Then I decided I didn’t need one enough to buy one. So now I have some power resistors and a calculator and make do. This quickly evolved into “stop buying things you need a load for” 

I can live without a proper electronic load and have done so; my thinking around acquisition hasn't been too far from yours. The two things that drive me in wanting one actually both involve making the same measurement, namely measuring PSU recovery from a step/pulsed load change. Every time I get a new PSU and run through the verification routine in the manuals I feel a bit shabby that I skip the step that verifies regulation, excursion and settling time from a step load change. I also have a long standing 'to   do   complete' which is to design and build some really pukka linear bench PSUs - I'll need to make the same measurements in verifying/refining my designs for these.

Start there, and then add the thinking "While I'm at it, I ought to do a proper job and add constant resistance for battery testing. Oh, and if I'm going to bother with that, I ought to do constant power too.". This may be an example of the best being the enemy of the good.

If you dig around in very old HP manuals, circa 1960s, at the verification stuff in there, they tend to use a mercury wetted relay and a power resistor of some sort. Probably fine.

For me, I usually test it like this unscientifically:

1. Connect suitably sized power resistor across output.
2. Connect (digital) scope across output and set it to trigger just under the peak in single shot mode.
3. Turn it on.
4. Not worry too much about other step changes

[mnementh]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

The quick version is that a 50Ω has more dielectric in the male plug, where the 75Ω is just air.

Also, there's a thread on this forum discussing it. I mean: Apparently, there are other threads on this forum... 

"Jetzt, wo du es sagst, sehe ich es auch."   

None that matter.

mnem
Sorry... I can't see them.  

[tggzzz]

Cheap HV probe on ebay this morning. 26$

https://www.ebay.com/itm/BECKMAN-INDUSTRIAL-HV231-22-HIGH-VOLTAGE-PROBE/274689423954

I don't like the hook on the end. When measuring HV my mantra is get on and get off ASAP. With that hook you could easily get hung up. 

Hang it on, move away, turn it on, measure, turn it off, move in, unhook it, have a beer.

[ch_scr]

... As it doesn't have an UI, one needs an old W95 laptop to run the original software. For this reason, I rarely use it.

All I see is a serial port, any reason the software won't run in a virtual machine on a modern system? The USB2Serial will go into the VM just fine.

[25 CPS]

Cheap HV probe on ebay this morning. 26$

https://www.ebay.com/itm/BECKMAN-INDUSTRIAL-HV231-22-HIGH-VOLTAGE-PROBE/274689423954

That tempted me at first glance but looking at the label on the handle, it's designed to pair with a 22 M\$\Omega\$ input impedance meter.  I can't think of one offhand that's suitable to pair with that probe.  At least, I know for sure I don't have something that would work correctly with that.  Maybe that's the reason for the price?

[med6753]

Well I'm back and now cruising along at a snappy 221mbps. I can now leap tall buildings in a single bound. 


The install did have one "gotcha" but we figured it out.   

[mnementh]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

      You can tell them apart by the reduced or missing dielectric, like this random 75 Ohm BNC Tee.

https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg3369696/?topicseen#msg3369696

There was also some discussion in here aboot this a while back; the specification for 75Ω BNC appears to also include a different diameter center pin, which is not always adhered to. I ran into this with some of my Crestron service calls back in the day; a BNC that had the center socket damaged by insertion of the wrong type BNC plug and no longer made proper contact.

IMO that may be the most important reason not to confuse the two, or arguably to not have 75Ω BNC anywhere near your work if you don't have to; the chance that you might accidentally do that damage to a good bit of gear if you forget on something you "just knocked together with what you have lying around".

IME, out in the wild that mismatch appears to be in many cases ignored nowadays; I've seen more than a few cheap imported AV bits & bobbles that use 50Ω BNCs (or at least, what appears to be 50Ω... maybe they use a dielectric that makes it a moot point in those applications...? ) for various video interconnects, and cheap NTSC/PAL cameras are pretty much a crapshoot too. Not sure if that is 1/10th of a penny-pinching or complete ignorance; probably a mix of the two. 

mnem
 

[capt bullshot]

... As it doesn't have an UI, one needs an old W95 laptop to run the original software. For this reason, I rarely use it.

All I see is a serial port, any reason the software won't run in a virtual machine on a modern system? The USB2Serial will go into the VM just fine.

TBH, I couldn't be bothered to try it.
Additionally, if one wants the graphs displayed at reasonable speed, on should use the parallel port connected to the printer port, with the application SW directly talking to the printer port HW.  I remember, one could manage the SW to run on NT and maybe even Win 2k, using some driver that enabled userland port I/O.

The serial comm sometimes stalls for unknown reasons, don't know if this gets better with USB2serial in a VM, so the parallel mode is preferred. I've seen many issues with serial ports on windows in general, and with serial through USB too.

[Cerebus]

If you dig around in very old HP manuals, circa 1960s, at the verification stuff in there, they tend to use a mercury wetted relay and a power resistor of some sort. Probably fine.

More than fine. The edge speed you can get with a decent mercury wetted relay is scary, you start talking about measuring it in nanoseconds or picoseconds; no electronic load is going to keep up with that. I've even considered going down that route, but the flexibility of an electronic load is attractive compared to the limited ranges one could test with switching discrete resistors or combinations thereof. If you hook 'em with test leads you're wasting a lot of the good with lead inductance, if you make a proper box of resistors, switches and heatsinks to keep the inductance nice and low you're back into building something proper and might as well go down the building an electronic load route (unless you really want those insanely short switching times).

Argh, too many choices, too many tradeoffs.  Maybe I'll go back to hovering, vulture like, over eBay. 

[Cerebus]

Well I'm back and now cruising along at a snappy 221mbps. I can now leap tall buildings in a single bound. 

Provided that they are made out of Lego. 

[med6753]

 

Well I'm back and now cruising along at a snappy 221mbps. I can now leap tall buildings in a single bound. 

Provided that they are made out of Lego. 

 

[Cerebus]

There was also some discussion in here aboot this a while back; the specification for 75Ω BNC appears to also include a different diameter center pin, which is not always adhered to. I ran into this with some of my Crestron service calls back in the day; a BNC that had the center socket damaged by insertion of the wrong type BNC plug and no longer made proper contact.

It does, and it has to. The impedance of a coaxial connector/cable is governed by:

\[ Z_0 = \frac{138\ log{\frac{D}{d}}}{\sqrt{\epsilon_r}}\]

where \$Z_0\$ is the characteristic impedance, \$D\$ is the diameter of the outer conductor, \$d\$ is the diameter of the inner conductor and \$\epsilon_r\$ is the relative permeability permittivity of the dielectric. As the outside diameter is fixed by the connector geometry it follows that to get the desired impedance the diameter of the inner conductor, the pin, has to change.


edit: permeability permittivity - I'm always getting that one wrong. I blame the people who decided that electromagnetism needed two parameters that shared more letters than they differed by.

[mnementh]

I am aware of this. I'm weak in the math, but I understand the principles involved. I also know that in many cases, as per the discussion I linked to, the specification is not adhered to very well. EDIT: I also understand that is primarily due to a combination of short cable length and low frequency and low-power signal making it possible to get away with that misuse.

The advent of PTFe-dielectric cable and connectors has made some difference here; the near-neutral near-ideal velocity factor thereof makes the calculations we use for making a SMA feed-cable on our RC transmitters, for example, a little simpler.

mnem
 

[mansaxel]

IME, out in the wild that mismatch appears to be in many cases ignored nowadays; I've seen more than a few cheap imported AV bits & bobbles that use 50Ω BNCs (or at least, what appears to be 50Ω... maybe they use a dielectric that makes it a moot point in those applications...? ) for various video interconnects, and cheap NTSC/PAL cameras are pretty much a crapshoot too. Not sure if that is 1/10th of a penny-pinching or complete ignorance; probably a mix of the two. 

(warning, this is after half a bottle of Domaine du Pesquier Gigondas, something you all should try, it's a really good wine, and the PDF is in French because I'm a right bastard, so there.)

What I was hinting at with my Canford reference upthread is that a lot of video companies preferred 50Ω connectors which was A-OK back in the days of PAL or Never Twice Same Color or Sometimes Each Camera Assumes Maturity and somewhat so in  SMPTE 259M Standard Definition digital video, simply because the 50Ω plug is sturdier and there are a lot of 200lb gorillas in the video business.

[Ero-Shan]

Here a similar and maybe older intrument: Dual +-50.00V or +-9.999V, 1.5A.
Manual control via mouse piano.
GPIB programming is a nightmare: Enter a code, then enter a digit, after entering all digits enter the code to shift it into the DAC.

The 2 quadrant output is certainly not bad. But the mouse piano is really awful. Do you use it often?

Today I put it through the adjustment procedure. After finishing up, I thought that I'd probably never had a use for it. Half an hour later, I suddenly realized that it might be exactly what I needed for my heat sink tests.
The day was too short though, hope I can do them next weekend.

[Why is you image gone?]

[mnementh]

mnem
Current mood: DIP-py.