Topics

Scope grounding and generators


Roy Thistle
 

On Tue, Oct 27, 2020 at 06:39 PM, Robert Simpson wrote:


I have a Fluke DMM, model 8024B (the one with buttons along the left side)
that has a max reading save option.
Again, if you use the meter to sample a few tens of cycles of an AM pure sine wave your fluke will tell you the peak RMS value of the envelope.
You could use your meter's peak hold function to give you some indication of the peak voltage the generator is putting out... but, my guess is that the AVR is working... and will stop high excursions... but won't stop the voltage from drooping, under heavy surges, or heavy loads. (Usually, if the AVR is bad... there is no output from the generator.)
Thus, what you need is a TRMS meter with a Min Max function.


Robert Simpson
 

OK, I just bought an inexpensive TRMS meter with good reviews. Arrives in a couple of days. Very interested in what that shows. Also, I bought the generator used. It ran rough at first. Replaced the fuel system, and now it runs smooth and steady.
Bob


Roy Thistle
 

On Tue, Oct 27, 2020 at 06:39 PM, Robert Simpson wrote:


an isolation transformer
They are saying use a "filament" transformer because that takes 120 VAC to a much safer 6 or 12 VAC, along with the isolation, from the primary, to the secondary, that a transformer provides.
An isolation transformer just isolates...for example, takes 120 VAC to 120 VAC. But then you are still having to deal with a relatively high voltage.


Greg Muir
 


Chuck Harris
 

Thanks Greg! Your links should at the very least explain why
generators can be a problem.

I long ago concluded that brushless generators were death for
devices that need clean power. It is one thing to use a big box
generator to run a few portable circular saws and drills, and
quite another to use one to run a house with its myriad of
switching power supply type loads.

A suggestion was made to use an UPS, like the APC Smart UPS.
This on the surface seems like a good idea, but it falls apart
when you come to realize that the UPS is only a standby supply,
and as such can only generate power for 15 or 20 minutes before
it will be seriously hot.

Thanks for the links.

-Chuck Harris

Greg Muir via groups.io wrote:


Stephen Hanselman
 

Bob,

On your generator observation. If this is a modern AC source if it high isn’t more likely to be a field voltage issue? Too fast should change frequency, I think...

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Oct 27, 2020, at 18:39, Robert Simpson via groups.io <go_boating_fast=yahoo.com@groups.io> wrote:

First, a question came up about my background.
With a year of military training I was a radio repair tech in the Army, both tube and transistor equipment. I worked my way through college (business degree) working with the university electric shop under the direction of certified electricians. We did ever thing from wall outlets, motors to building main panels. I still have my half inch conduit bender. I have been repairing Tek scopes, computer monitors, TVs etc. as a hobby for over ten years now including HV supplies in 7603s and a 7904. I have appropriate HV probes. My professional life was in Information Technology from early DEC mini computers to finally leading development teams building custom web data base business applications as a PMI certified project manager. Generators are new to me.

Moving on,
A little bit of progress. I have good ground wire set up. After the comment about the ground being 3/16”, I found a short piece of copper tubing with a 3/16 OD. By soldering the end of an insulated wire into a short section of tubing, I can push the tubing into the grounding hole part of a socket with no open wire exposed. As the tubing fits snugly, I have a protected secure connection. The other end of my wire is screwed into the ground lug of the generator.

Since the generator puts out distorted AC, I am curious about max volts. I have a Fluke DMM, model 8024B (the one with buttons along the left side) that has a max reading save option. So I am thinking of some experiments. Such as what is max volts when first starting the generator. What is the max volts when running with no load. What is the max volts when under some load.

The suggestion about isolating the scope through a transformer got me thinking about a voltage spike damaging the scope. I did probe my house power using a connected socket the scope is plugged into at my bench. I used a P6006 with 6 foot cable. Checking the P6006 on the calibrator signal showed a very clean square wave. Then using the 50V setting I checked house power. Not surprising, there is a very clean sine wave of about 350V P-P and a 60Herz frequency.

Also, would an isolation transformer (which I have somewhere around the house, Haven't used it in awhile) be just as good as a filament transformer (which I don't have)?

Note: All this effort is only meant for a couple of test runs. I have no plans of ongoing monitoring. I think my generator is running a little fast as my DMM shows 132V as compared to my house voltage of about 121V. Would a wonky sine wave of the generator affect the DMM reading?

So the scope can show me the frequency. If the generator is running fast, I will need to adjust the governor. If the frequency is correct then maybe the voltage regulator is off. And of course I am curious about just what kind of sine wave the generator puts out. I don't have a frequency meter as I haven't needed one until now.

Bob





Paul Amaranth
 

On Wed, Oct 28, 2020 at 09:40:29AM -0400, Chuck Harris wrote:
A suggestion was made to use an UPS, like the APC Smart UPS.
This on the surface seems like a good idea, but it falls apart
when you come to realize that the UPS is only a standby supply,
and as such can only generate power for 15 or 20 minutes before
it will be seriously hot.

Thanks for the links.

-Chuck Harris
Even using the UPS as a "filter" between the generator and equipment
has problems. The UPS may decide the generator supplied power is not
clean enough to run on line and may just stay on batteries and you're
back to your short run time.

I have a large (3KVA) UPS running a server rack that will not go off
battery if I have my backup generator running (16KVA, not small). The
generator has a mechanical speed govenor and runs at 62Hz until about
40% load when it gets pulled down to 60Hz. 62Hz is too far off my
UPS's idea of clean power. I have a project to replace that with an
electronic govenor that is more responsive to load. But right now I have
to shut all the computers down when I get an extended power failure.

Paul

--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows


Roy Thistle
 

On Wed, Oct 28, 2020 at 06:40 AM, Chuck Harris wrote:


UPS is only a standby supply,
and as such can only generate power for 15 or 20 minutes before
it will be seriously hot
Nope, unless you buy it from Wally's.
15 or 20 minutes ought to refer to the time it takes the battery, in smaller cheap units, to discharge.
Heat ought to refer to ill-designed cooling, or density.
UPS is rated the same as any other SMPS... as long as there is DC input... or battery power.
Here in the colonies, there are plenty in the junk yards, and in possession of industrial bottom feeders that would run continuously for years, subject to the above considerations.

Here in the colonies.... there are plenty of old


Chuck Harris
 

I have been in involved in the scrapping of thousands of
commercial grade UPS's from a lot of different manufacturers.

There are two general varieties. The Standby UPS, and the
True UPS. The standby UPS comes on when the power quality
reaches a certain level of degradation. The true UPS supplies
the load's power continuously from its inverter.

True UPS's can produce power continuously, as that is what
they are designed to do. Standby UPS's are generally designed
with only enough cooling to supply power until the internal
battery is exhausted.

The True UPS is typically very heavy, has a strong fan that
runs all the time. They also generates a lot of heat. The
Standby UPS only makes noise and generates heat when the power
is bad.

I would guess that we get 100 Standby UPS's for every True UPS.

Which makes sense. Why would anybody want a machine under
their desk that gets hot, wastes power, and sounds like a
vacuum cleaner?

-Chuck Harris

OBTW Roy, I am pretty sure that nobody cares that you are a
colonial. I asked some ants that invaded a scrap UPS, and
they said, "Isn't everybody?"

Roy Thistle wrote:

On Wed, Oct 28, 2020 at 06:40 AM, Chuck Harris wrote:


UPS is only a standby supply,
and as such can only generate power for 15 or 20 minutes before
it will be seriously hot
Nope, unless you buy it from Wally's.
15 or 20 minutes ought to refer to the time it takes the battery, in smaller cheap units, to discharge.
Heat ought to refer to ill-designed cooling, or density.
UPS is rated the same as any other SMPS... as long as there is DC input... or battery power.
Here in the colonies, there are plenty in the junk yards, and in possession of industrial bottom feeders that would run continuously for years, subject to the above considerations.

Here in the colonies.... there are plenty of old






Roy Thistle
 

On Wed, Oct 28, 2020 at 10:13 AM, Paul Amaranth wrote:


The UPS may decide the generator supplied power is not
clean enough to run on line
Yes, they will do that. Some are more fussy than others.
As you pointed out, for a non-inverter generator, you need to spec. a nominal load. A generator and a battery bank, in the context of this discussion is not meant for long term continuous duty... however you spec that. Nothing wrong with batteries, if you spec it right, and realistically.
Here in the colonies, the local power provider specs +- 0.5 % from 60Hz nominal... as per the NPPC Directory 12. That's as bad as line power frequency variation could get? Maybe not. But in the long run for power grid interoperability that's the standard they are quoting.
1% would be good?... good enough for me (I don't use/recommend power line frequency as a frequency standard.) 2% is okay? I think some UPS will still operate within 1%; but, maybe not... the newer ones are better.
And just to point it out (which I sure you already know; but others might be missing?)... inverter generators are... well they are just a DC power source, running a kind of UPS.


Greg Muir
 

Chuck,

In days of yore when power supplies were basically linear it was a simple approach to use any type of AC supply available. Switchers sort of changed that scenario to a certain degree.

There are people out there who aren’t aware that most of the early UPS units (and still some from today’s production) have square wave outputs. I have not seen any equipment that disliked that waveform but mostly worry about the high risetimes, overshoot and the stress on power supply components. It is obvious that computers and peripherals seemed to have tolerated that Draconian waveform over the years.

Simulated sine wave UPS units was a more progressive step in the right direction until “pure” sine wave units came along. But I place quotes around “pure” since those, too aren’t so precise with regards to distortion. I guess if one tricked a UPS unit by modifying it into running constantly or procured an online unit and placing either one between the generator and the load they would have a happier arrangement given any distortion produced from the generator itself. But those pure sine wave output UPSs do carry a significant quiescent current draw.

There was one instance several years ago when I was called on to do some RF field testing whereby I connected my spectrum analyzer to a small square wave 12/115V inverter for power. It worked well with no problems but I felt uncomfortable with the 60 Hz noise emanating from the analyzer’s power supply having to deal with the nasty waveform. So I picked up a true sine wave inverter before the next trip out. When on my next outing I connected my new inverter to the spectrum analyzer and things sounded a whole lot better. But much to my surprise the entire RF spectrum of interest was filled with inverter noise!! The problem was eventually rectified by placing the inverter in a shielded enclosure with heavy high frequency filtration on both the 12V input & 115V output leads.

There was one time I was doing engineering for a scientific organization where we were modifying cargotainers to house scientific equipment and living quarters for the scientific staff to drop on the decks of research ships for their use. It was known that the AC power provided by the ship’s supply was rather horrid with regards to noise, transients and other anomalies (something akin to the power found on railroad locomotives). So we procured several large AC-AC converters where the incoming power was rectified to DC (linear-wise) then applied to crystal controlled DC-AC sine wave converters to provide pure power for the instrumentation and other facilities. The system was a real power hog and occupied a lot of space but everything worked well. Besides, the ships have boundless amounts of power to keep things going anyway.

As I mentioned previously I cannot speak of any experiences where the quality of the incoming AC power has jeopardized the operation of my equipment but I am always cautious when coming up against unusual circumstances and will take measurements where necessary to guarantee satisfactory operation. A few simple measurements takes far less time that repairing broken equipment.

Greg


Roy Thistle
 

On Wed, Oct 28, 2020 at 10:59 AM, Chuck Harris wrote:


Roy, I am pretty sure that nobody cares that you are a
colonial. I asked some ants
Well in the parlance, the claim that: "There is not one person ("body"), such that that person("body") cares (your vernacular) that that person ("body") is a colonial."... that claim is false. Proof: I care.
If you limit your universe of discourse to the Tekscopes forum, the claim is still false. (Same proof.) If you interpret your claim within the vernacular, the claim is in-consistent... as given.
As for ants... Peng Lei style at most... well... one person may wax metaphorical, even poorly so... yet deny the legitimacy of others to do so.
As for UPS et. al., under-cover, or by the label...yes, they come and go out of the computer center(s)/server-room... and more than a few have been scrapped.


Chuck Harris
 

And yet, still nobody cares.

More and more I come to realize that ignoring
you completely is a very good policy.

-Chuck Harris

Roy Thistle wrote:

On Wed, Oct 28, 2020 at 10:59 AM, Chuck Harris wrote:


Roy, I am pretty sure that nobody cares that you are a
colonial. I asked some ants
Well in the parlance, the claim that: "There is not one person ("body"), such that that person("body") cares (your vernacular) that that person ("body") is a colonial."... that claim is false. Proof: I care.
If you limit your universe of discourse to the Tekscopes forum, the claim is still false. (Same proof.) If you interpret your claim within the vernacular, the claim is in-consistent... as given.
As for ants... Peng Lei style at most... well... one person may wax metaphorical, even poorly so... yet deny the legitimacy of others to do so.
As for UPS et. al., under-cover, or by the label...yes, they come and go out of the computer center(s)/server-room... and more than a few have been scrapped.


 

May I suggest that the subject of many of these posts should be changed to Switching Mode Power Supplies

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Greg Muir via groups.io
Sent: Wednesday, October 28, 2020 12:21 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Scope grounding and generators

Chuck,

In days of yore when power supplies were basically linear it was a simple approach to use any type of AC supply available. Switchers sort of changed that scenario to a certain degree.

There are people out there who aren’t aware that most of the early UPS units (and still some from today’s production) have square wave outputs. I have not seen any equipment that disliked that waveform but mostly worry about the high risetimes, overshoot and the stress on power supply components. It is obvious that computers and peripherals seemed to have tolerated that Draconian waveform over the years.

Simulated sine wave UPS units was a more progressive step in the right direction until “pure” sine wave units came along. But I place quotes around “pure” since those, too aren’t so precise with regards to distortion. I guess if one tricked a UPS unit by modifying it into running constantly or procured an online unit and placing either one between the generator and the load they would have a happier arrangement given any distortion produced from the generator itself. But those pure sine wave output UPSs do carry a significant quiescent current draw.

There was one instance several years ago when I was called on to do some RF field testing whereby I connected my spectrum analyzer to a small square wave 12/115V inverter for power. It worked well with no problems but I felt uncomfortable with the 60 Hz noise emanating from the analyzer’s power supply having to deal with the nasty waveform. So I picked up a true sine wave inverter before the next trip out. When on my next outing I connected my new inverter to the spectrum analyzer and things sounded a whole lot better. But much to my surprise the entire RF spectrum of interest was filled with inverter noise!! The problem was eventually rectified by placing the inverter in a shielded enclosure with heavy high frequency filtration on both the 12V input & 115V output leads.

There was one time I was doing engineering for a scientific organization where we were modifying cargotainers to house scientific equipment and living quarters for the scientific staff to drop on the decks of research ships for their use. It was known that the AC power provided by the ship’s supply was rather horrid with regards to noise, transients and other anomalies (something akin to the power found on railroad locomotives). So we procured several large AC-AC converters where the incoming power was rectified to DC (linear-wise) then applied to crystal controlled DC-AC sine wave converters to provide pure power for the instrumentation and other facilities. The system was a real power hog and occupied a lot of space but everything worked well. Besides, the ships have boundless amounts of power to keep things going anyway.

As I mentioned previously I cannot speak of any experiences where the quality of the incoming AC power has jeopardized the operation of my equipment but I am always cautious when coming up against unusual circumstances and will take measurements where necessary to guarantee satisfactory operation. A few simple measurements takes far less time that repairing broken equipment.

Greg







--
Dennis Tillman W7pF
TekScopes Moderator


Roy Thistle
 

And yet, I do.
If anyone chooses to ignore, then I'll have less to read, less to ponder, and less to write about.
Go ahead make your day, if that's what makes it a better day for you.
My day has certainly been better for participating in TekScopes.


Robert Simpson
 

Getting back to a Tektronix question, I have P6009 probes. Wouldn't using those be safe from over voltage outputs (If there are any) of a generator to the 465M oscilloscope?
Bob


Roy Thistle
 

On Wed, Oct 28, 2020 at 09:15 PM, Robert Simpson wrote:


I have P6009 probes.
P6009 is rated to 1.5 KV. And for 60 Hz nominal frequency doesn't need to be derated. (It's flat to around 100 KHz.) The can be compensated to the 465's input capacitance.
So yes and no.
Your generator isn't new, so if there is a problem with the AVR, the voltage could rise significantly...there could be an over-voltage problem... but, surely not so much that a P6009 wouldn't protect the 465 inputs.
I'd be more worried about high voltage transients finding their way into the scope inputs.
I'd be more concerned about that when the generator is started, stopped, stalls, or is driving inductive loads.
Maybe run a couple of trouble lights, fitted with incandescent bulbs, when the generator has been running well for a while, and is well warmed up. (The bulbs are a very crude indication of frequency drift, and voltage drift, or over-voltage, or under-voltage.)
I'd do a 465/P6009 measurement on the above... if I had to.


stevenhorii
 

I wonder whether optical isolation would work. The photodiode types have
very fast response, but can be nonlinear. Though usually used for logic
signals, there are optocouplers designed for analog signals. Some have a
more complex circuit that compensates for diode nonlinearity. For an AC
input, there are some with two diodes so conduction will occur across one
of the diodes during the AC cycle.

A really fast response optocoupler designed for AC input would likely
preserve any higher-frequency components of the input signal.

An opto isolator is likely a lot less expensive than a scope so destroying
it from overvoltage input would save, at a minimum, having to replace scope
input overvoltage protection elements.

Just a thought. I have noted that opto isolators are used in medical
equipment so the patient is isolated from the high voltages that may be
present in the instruments.


On Thu, Oct 29, 2020 at 02:06 Roy Thistle <roy.thistle@mail.utoronto.ca>
wrote:

On Wed, Oct 28, 2020 at 09:15 PM, Robert Simpson wrote:


I have P6009 probes.
P6009 is rated to 1.5 KV. And for 60 Hz nominal frequency doesn't need to
be derated. (It's flat to around 100 KHz.) The can be compensated to the
465's input capacitance.
So yes and no.
Your generator isn't new, so if there is a problem with the AVR, the
voltage could rise significantly...there could be an over-voltage
problem... but, surely not so much that a P6009 wouldn't protect the 465
inputs.
I'd be more worried about high voltage transients finding their way into
the scope inputs.
I'd be more concerned about that when the generator is started, stopped,
stalls, or is driving inductive loads.
Maybe run a couple of trouble lights, fitted with incandescent bulbs, when
the generator has been running well for a while, and is well warmed up.
(The bulbs are a very crude indication of frequency drift, and voltage
drift, or over-voltage, or under-voltage.)
I'd do a 465/P6009 measurement on the above... if I had to.






Chuck Harris
 

They should be ok, as long as you are using only the probe
tips, and not the grounding clips to connect to the line and
neutral leads of the generator. The probe grounding clips
should connect to the frame ground for the generator, which
should be connected to the same ground as your scope's chassis
ground.

That means, you use the scope's "ADD" mode, and set CH2 to
invert. Both channel attenuators are set to the same value.

Your scope can survive pretty much anything that your DVM
can handle... as long as you don't exceed the scope's rating
of 500V (DC + Peak AC) derated with frequency: 30V to 50MHz,
and 27V to 100MHz.

Usually, my recommendation is don't exceed the scope's maximums
regardless of the probes "enhancements" to those maximums, but
obviously there have to be exceptions to that very conservative
rule.

At issue is if the probe breaks down internally, it can damage
the scope through over voltage, if the probe is exposed to
voltages that exceed the scope's maximums.

Filament transformers are cheaper than a repair on your scope's
front end, and will reveal everything that matters on your
generator's output signal.

A second thing about instrumentation. When you are measuring
stiff power sources, you need to take stiff protection measures.
When you are measuring weak power sources, weak protection
measures will suffice.

Your generator is a fairly stiff power source. It can dump
way more than 4000W into a dead short circuit.

-Chuck Harris

Robert Simpson via groups.io wrote:

Getting back to a Tektronix question, I have P6009 probes. Wouldn't using those be safe from over voltage outputs (If there are any) of a generator to the 465M oscilloscope?
Bob






Chuck Harris
 

You have to ask yourself what you want to see.

If you want to know the distortion of the "sine wave", you only
need at most DC to a few kilohertz of bandwidth.

If you want to know the RF on the generator's output, then stop
looking at the 60Hz component, and put a capacitor in series with
the generator, and look only at the HF components.

-Chuck Harris

stevenhorii wrote:

I wonder whether optical isolation would work. The photodiode types have
very fast response, but can be nonlinear. Though usually used for logic
signals, there are optocouplers designed for analog signals. Some have a
more complex circuit that compensates for diode nonlinearity. For an AC
input, there are some with two diodes so conduction will occur across one
of the diodes during the AC cycle.

A really fast response optocoupler designed for AC input would likely
preserve any higher-frequency components of the input signal.

An opto isolator is likely a lot less expensive than a scope so destroying
it from overvoltage input would save, at a minimum, having to replace scope
input overvoltage protection elements.

Just a thought. I have noted that opto isolators are used in medical
equipment so the patient is isolated from the high voltages that may be
present in the instruments.


On Thu, Oct 29, 2020 at 02:06 Roy Thistle <roy.thistle@mail.utoronto.ca>
wrote:

On Wed, Oct 28, 2020 at 09:15 PM, Robert Simpson wrote:


I have P6009 probes.
P6009 is rated to 1.5 KV. And for 60 Hz nominal frequency doesn't need to
be derated. (It's flat to around 100 KHz.) The can be compensated to the
465's input capacitance.
So yes and no.
Your generator isn't new, so if there is a problem with the AVR, the
voltage could rise significantly...there could be an over-voltage
problem... but, surely not so much that a P6009 wouldn't protect the 465
inputs.
I'd be more worried about high voltage transients finding their way into
the scope inputs.
I'd be more concerned about that when the generator is started, stopped,
stalls, or is driving inductive loads.
Maybe run a couple of trouble lights, fitted with incandescent bulbs, when
the generator has been running well for a while, and is well warmed up.
(The bulbs are a very crude indication of frequency drift, and voltage
drift, or over-voltage, or under-voltage.)
I'd do a 465/P6009 measurement on the above... if I had to.