Use Local Voltage To Sense Remore Voltage (Meter)

[MEXICOWANDERER]

http://www.buyincoins.com/item/26013.html#.V0yNGeSG9_k

This link takes you to an accurate digital voltmeter. One of the problems with using a remote mounted meter, is that it reports what it see's, no matter how severe the voltage drop. This meter uses local power to light the LED segments, and remote sensing to read power AT THE BATTERIES. Or panels (to 33 vdc) or converter, or inverter input, alternator output stud, ignition feed, or whatever you wish to monitor.

This critter makes an utter laughingstock out of the "accuracy" of 3-1/2 digit voltmeters.

Sure it's expensive - way beyond the reach of most of us. But when money is no object...

[MEXICOWANDERER]

I traded three months of labor designing a 67 Kv, 800Kw hydroelectric project to integrate with a Southern California Edison transmission line. The project owner (foolishly IMO) jumped at the chance of "Buying An Oscilloscope" in lieu of payment. He must have figured annual proportional tax depreciation would work wildly in his favor. I presented a legal contract specifying the make and model and "new, not reconditioned or seconds". The guy definitely did not get screwed. I saved him about $50,000 in transformers, concrete rather than wood transmission poles and even 90% on the cost of the insulators.

My unit is 100% solid-state. Quad color trace with USB interface. It was made for Sandia Labs, which took delivery of it, made a formal complaint it did not meet GSA contract specifications. I drove to New Mexico and with a bank Cashier's Check, went through a few miles of jumping GSA hoops and took delivery. It's power supply can use 120-240-277-480 VAC 60 or 400 Hz. God help me if it ever breaks. it is protected in a 10 mil "Caltrans" orange trash bag along with 5 lbs of silica gel. Tied with four 11" cable ties 🙂

I did the same type of horse trading with a battery OEM. Three months or testing in exchange for a 6-3/4 digit bench multi-meter with 4-wire Kelvin Bridge, the 4 Kyocera solar panels, 1 100 kg digital platform scale with 1 gram resolution, a 4024 Trace inverter, and one free ticket trip to the Lockheed Skunk Works disposal auction. In turn the OEM received the "Irrefutable Proof" of performance he craved. The ratio of trading versus payment roughly translated to 320% increase in value. he he he.

[LScamper]

I used a Tektronix 556 for many years (531 before that). Moved up to Tektronix 7904 and 7834. Used these for about 20 years before getting a digital Tek scope. The price of the 7904 and 7834 with plug-ins was about $45,000 each in todays dollars. The DC accuracy was about 2 percent.

Anyone remember the Tektronix 519 1Ghz scope?

My scope at home after retiring is a Rigol 1102E. the bandwidth is only 100Mhz as compared to 400 and 500 Mhz of the Tek scopes. But every thing else is far better and it cost only about $400.

Fluke meter DC accuracy can be about .2 percent to about .005 percent depending on how much you want to spend.

[PaulJ2]

Oh the memories! Worked at Tektronix for 38 years, now retired. Calibrated and repaired 7704A, 7904, 7104, and all associated amplifier and time base plug-in modules.
Still have a Tek 465 portable scope and am holding in my hand a Tek DMM157 meter given to me when i retired.
Blows fuse? Probably dried out large filter caps-230 MFD- if i remember correctly. Drew- if you have a variac run it up slowly and they may reform.
Ooops dang it, I'm retired!

[SCVJeff]

Allot of Tek scopes have "calibrated" pulse width and voltage test posts on them. However close even they are..

[MrWizard]

my O'scope is transistorized portable 25yrs old maybe older, and buried under the sofa where it has been for almost 6 yrs
it was 10mhz $1000? mini wonder when i got it

[DrewE]

The meter is a Fluke 73 series II -- nothing extraordinary there. According to the service manual for the meter, the error is 0.4% +/- one digit for DC voltage, and 2% +/- 2 digits for AC voltage from 45 Hz to 500 Hz (lowest range) or 1 kHz (other ranges). It's a 3 1/2 digit meter.

I'm not suggesting that the meter is exceptionally accurate, but rather that my oscilloscope is not, and in my experience (and to my understanding) oscilloscopes in general are likewise limited in their accuracy. You may observe I said nothing about the accuracy of your oscilloscope in particular. The 7704A is an old-school analog mainframe scope with plug-in amplifiers and timebases, and according to its service manual should be calibrated (the mainframe) to approximately 1% for the vertical amplifiers. I don't have the actual specifications on its accuracy. I do know that I would struggle to observe out much better than 2% error from the graticule on the CRT. In its current state, it's nowhere near properly calibrated, but that's immaterial here...I'm assuming it were operating in top-notch form. (Being an older analog scope, there are no nifty aids like cursors with readouts. It does have on-screen display of the vertical and horizontal gain settings, generated with some analog magic.)

Many DSOs are based around 8-bit A/D converters, which sets an absolute limit to their accuracy of about 0.5% at full scale simply due to quantization errors. High-resolution DSOs may indeed be more accurate than run-of-the-mill decent multimeters, assuming the rest of their signal chain is up to snuff. (What's the precision of a typical 10x scope probe? A basic Tektronix passive 10x probe (TPP0200) lists the input impedance +/- 1.5%....

Oscilloscopes are, of course, very versatile and useful tools, and can measure and show things that are absolutely impossible to do with a multimeter. But, by and large, they are not really suited for highly precise measurements.

I did just dusted off my scope and plugged it in and turned it on for the first time in awhile, and it promptly blew the line input fuse. 😞 I guess I have some troubleshooting to do in my copious free time.

[MEXICOWANDERER]

Fascinating DrewE 🙂

Care to share the Fluke model number and % error + - noted?

I spend an enormous amount of money to maintain my scope in calibration. They do drift and cross correlation of resistance to voltage is one way to detect error.

I see some $5K Fluke instruments out there. Clumsy me - I transport hand-held instruments within sloshy dinghies in a very corrosive atmosphere. Perhaps it's time to obtain a floating airtight case and load it with silica gel packets. I wish cheapskate manufacturers would consider gold plating vulnerable contacts. Computer OEMS do so with card-edge contacts and plugs. If I could keep stuff safe, environmentally, I would consider upgrading my hand held instruments.

Thank you for your reply. It made a considerable impression on me...

[DrewE]

MEXICOWANDERER wrote:

TWELVE VOLTS is the power supply for this PANEL meter. It is not hand-held.

The MEASUREMENT CIRCUIT is an entirely different portion of the meter. It will measure from 0.000 to 33.0 volts.

Absolutely different than standard 12-volt PANEL meters, this one can measure voltage DROP. It is not meant to substitute running around with a 9-volt battery hand held meter, measuring voltage drop.

But it WILL measure voltage DROP between batteries, between battery banks, between bank and inverter, solar panel arrays to 33.0 volts. Voltage drop. Problems with MPPT and PWM controllers.

This particular meter would not be very good for measuring many of these voltage drops because the input is not isolated from the power supply. You would have to either have an isolated power supply for the meter (which is not too hard to come by these days for a few dollars), or else make your measurements with respect to a common ground and subtract manually.

MEXICOWANDERER wrote:

If anyone thinks their FLUKE meter is as accurate as a 100 MHz Tektronix oscilloscope or a hundred plus dollar array of 10ppm calibration resistors, please let me know.

The issue is over VALUE not superlative based quantification.

For making absolute DC voltage or current measurements, or similar AC measurements with clean sinusoidal waveforms, my Fluke meter is much more accurate than my 200 MHz Tektronix 7704A scope. I'm pretty sure that would be equally true even for newer DSOs.

[MEXICOWANDERER]

Accuracy expressed in percentile

PLUS or MINUS "X" numbers in the least significant digit column (that is the far right hand column for non techhie types).

TWELVE VOLTS is the power supply for this PANEL meter. It is not hand-held.

The MEASUREMENT CIRCUIT is an entirely different portion of the meter. It will measure from 0.000 to 33.0 volts.

Absolutely different than standard 12-volt PANEL meters, this one can measure voltage DROP. It is not meant to substitute running around with a 9-volt battery hand held meter, measuring voltage drop.

But it WILL measure voltage DROP between batteries, between battery banks, between bank and inverter, solar panel arrays to 33.0 volts. Voltage drop. Problems with MPPT and PWM controllers.

Panel meters are HARD WIRES. Connections are PERMANENT. Multiple points can be selected using a single pole rotary switch. TELEPHONE WIRE is plenty large enough to carry the few milliamps necessary for sensor connection.

No this PANEL meter is not for everyone. This is much like a person reading an article discussing a 30-year-old single malt Scotch. "Ewwwwww! I don't need it! What in the world would ANYONE want this for?"

Questions regarding the usability of such a PANEL meter are justified. Criticism must have a base in logic, not mere preference.

If anyone thinks their FLUKE meter is as accurate as a 100 MHz Tektronix oscilloscope or a hundred plus dollar array of 10ppm calibration resistors, please let me know.

The issue is over VALUE not superlative based quantification.

[MrWizard]

Harvey
We are discussing panel mount meters for permanent install,
Not hand held testers

[LScamper]

Understanding specifications.

Understanding specs

"Accuracy, Uncertainty, and Repeatability

Accuracy is often the differentiating specification between similar appearing models. DC accuracy is usually used for the "banner" specification since it is usually better than the accuracy for other functions. DC accuracies of better than ±0.1 percent are just now becoming available. Added to the percentage figure will be a specified number of counts (sometimes referred to as "digits") due to rounding error and noise limitations. For DMMs, accuracy is specified as percent of reading as opposed to percent of full scale as specified for analog multimeters. If possible, avoid use of the bottom ten percent or so of any range since accuracy is badly degraded there. It isn't the percentage error that is the problem; it is the effect of the number of counts deviation becomes substantially larger in proportion to the measured value."

So if the voltage to be measured is 14.8V and the meter meets the stated accuracy of .3 percent then:

14.8V x .003 = .0444 volts. The meter could read anywhere from 14.756 to 14.844, so much for the last three digits!

This paper also gives a good comparison of errors using an average reading meter and true RMS meter.

[SCVJeff]

THESE days, and mounted there it could easily be a DTV channel :h

[time2roll]

SCVJeff wrote:

smkettner wrote:
One digit is enough to tell me what is happening.

.5 ? :C

One decimal actually.



(this indicates still in absorption btw)

[CA_Traveler]

landyacht318 wrote:
How is it known this meter is indeed accurate? They do not seem to have a calibration pot.

Exactly. If I wanted to check the calibration I'd compare it to my Fluke and certainly not the other way around.

And I need 1 mV resolution for my RV??? Really???

Really someone expects this to be accurate to 1 mV??? Another Chinese junk????