zog
Senior Member
- Location
- Charlotte, NC
I'd just spend $2 on one of those DMM's that Harbor Freight has. No need for a fancy shmancy Fluke.
And what is the CAT rating on that?
Which one is right?
- Thread starter chris kennedy
- Start date
- Status
And what is the CAT rating on that?
Cavie
Senior Member
- Location
- SW Florida
Fulthrotl
~Autocorrect is My Worst Enema.~
- Occupation
- E
Fulthrotl
~Autocorrect is My Worst Enema.~
- Occupation
- E
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090217-1436 EST
Following is a useful reference, but not very complete:
http://cp.literature.agilent.com/litweb/pdf/5988-6916EN.pdf
They have a little discussion on true RMS techniques.
I have been doing some comparisons between my fluke 27 and 87 and the results are not quite as I would expect. This relates to how useful my diode resistor method is for verifying the reading of an AC voltmeter.
.
Following is a useful reference, but not very complete:
http://cp.literature.agilent.com/litweb/pdf/5988-6916EN.pdf
They have a little discussion on true RMS techniques.
I have been doing some comparisons between my fluke 27 and 87 and the results are not quite as I would expect. This relates to how useful my diode resistor method is for verifying the reading of an AC voltmeter.
.
brian john
Senior Member
- Location
- Leesburg, VA
As far as I am concerned if neither meter is calibrated then both are possibly wrong.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
I need something more accurate than than that. We bring many good size 3? services to life wired to NEC minimum requirements. I'm a huge fan of checking voltage before a load is applied and after.
I'd just spend $2 on one of those DMM's that Harbor Freight has. No need for a fancy shmancy Fluke.
You going to stick that thing between two lugs to test 480V?
weressl
Esteemed Member
Ideal accuracy (claimed): +/- 1.2%
Greenlee accuracy (claimed): +/- 1%
Greenle explanation:
Two AC measurement methods are average-responding RMS calibrated and true RMS-reading.
The average-responding RMS calibrated method takes the average value of the input signal after full wave rectification, multiplies it by 1.11, and displays the result. This method is accurate if the input signal is a pure sine wave. The Greenlee CM-800 is an average-responding meter.
The true RMS-reading method uses internal circuitry to read the true RMS value. This method is accurate, within the specified crest factor limitations, whether the input signal is a pure sine wave, square wave, triangle wave, half wave, or signal with harmonics. The ability to read true RMS provides much more measurement versatility. The Greenlee CM-850 is a true RMS meter.
The Waveforms and Crest Factors table shows some typical AC signals and their RMS values.The average-responding RMS calibrated method takes the average value of the input signal after full wave rectification, multiplies it by 1.11, and displays the result. This method is accurate if the input signal is a pure sine wave. The Greenlee CM-800 is an average-responding meter.
The true RMS-reading method uses internal circuitry to read the true RMS value. This method is accurate, within the specified crest factor limitations, whether the input signal is a pure sine wave, square wave, triangle wave, half wave, or signal with harmonics. The ability to read true RMS provides much more measurement versatility. The Greenlee CM-850 is a true RMS meter.
Sinusodial waveform: RMS value 100, Average Value 90.
So one perhaps displaying true RMS and the other displays average responding RMS calibrated.
Last edited:
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
Nope, just tried different combination and the results are the same. 114-125.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
Thank you Laszlo, but we have used both testers on the same services seconds apart in the past and the results were within a volt.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
I bought their ampclamp once, it wasn't accurate out of the box. Like, noticeably inaccurate based on common sense, right out of the box. It wasn't worth the $10. I'll shop at Harbor Freight for some things, but cordless drills and meters are no longer on that list.I'd just spend $2 on one of those DMM's that Harbor Freight has. No need for a fancy shmancy Fluke.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090217-2213 EST
chris:
Since your two meters previously read within about 1% of each other and now are about 8% apart, and the DC readings currently are within about 1/2 %, then it is quite possible that one of the true RMS converters has failed.
In a day or two you should expect to try the half wave rectifier test and if you do this at home you will probably have a moderately good sine wave.
I have a slightly top clipped sine wave at the shop, and I get a fairly good correlation predicting the AC value from the half wave averaged DC value. The clipping of that waveform is visible in my photo P5 at
www.beta-a2.com/EE-photos.html
This clipping is not from equipment in our building. I looked at it on Sunday when no significant equipment was on. Somebody in our area is drawing a lot of current in capacitor input filters off of the line.
I have done a calculation on a clipped sine wave at the 0.707 point and if there were no calculation errors, then it looks like this severe clipping only causes about a 10 % difference between an average reading AC meter and a true RMS meter. Much less clipping will produce less difference.
.
chris:
Since your two meters previously read within about 1% of each other and now are about 8% apart, and the DC readings currently are within about 1/2 %, then it is quite possible that one of the true RMS converters has failed.
In a day or two you should expect to try the half wave rectifier test and if you do this at home you will probably have a moderately good sine wave.
I have a slightly top clipped sine wave at the shop, and I get a fairly good correlation predicting the AC value from the half wave averaged DC value. The clipping of that waveform is visible in my photo P5 at
www.beta-a2.com/EE-photos.html
This clipping is not from equipment in our building. I looked at it on Sunday when no significant equipment was on. Somebody in our area is drawing a lot of current in capacitor input filters off of the line.
I have done a calculation on a clipped sine wave at the 0.707 point and if there were no calculation errors, then it looks like this severe clipping only causes about a 10 % difference between an average reading AC meter and a true RMS meter. Much less clipping will produce less difference.
.
IMM_Doctor
Senior Member
Add a 3rd meter
Add a 3rd meter
Can you duplicate that same picture at the same outlet today?
Above all of the exacting literature of RMS measurments, I am curious. Can you borrow a "third" meter yet, and have it at the outlet at the same time and capture the readings. You may find 2 meters agree.?
We work on industrial automation. When we find that an electrical transducer differs from a mechanical display, we typically introduce a 3rd measurment device temporarily to diagnose which measurment is more representative of the process.
Add a 3rd meter
Can you duplicate that same picture at the same outlet today?
Above all of the exacting literature of RMS measurments, I am curious. Can you borrow a "third" meter yet, and have it at the outlet at the same time and capture the readings. You may find 2 meters agree.?
We work on industrial automation. When we find that an electrical transducer differs from a mechanical display, we typically introduce a 3rd measurment device temporarily to diagnose which measurment is more representative of the process.
weressl
Esteemed Member
Now that would make me think that:
- Something is happened to one of the meters,
- There is a qualitative change in the measured parameter, and I can only think of harmonics.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090218-1149 EST
The Agilent 1253A list price is $449.
At http://www.transcat.com/Catalog/Pro...TRAPCD=WBGMM&gclid=CKroxIrD5pgCFSHaDAodfgJ5cQ
it is listed at $379.
Newark's price is $449 and 60 days lead time.
These people seem to have a 15% discount currently.
http://www.metrictest.com/catalog/promotion/agilent_hhdmm.jsp
I suspect availability is a problem from any source.
In Google the search string
1253a meter
seemed to be fairly useful.
.
The Agilent 1253A list price is $449.
At http://www.transcat.com/Catalog/Pro...TRAPCD=WBGMM&gclid=CKroxIrD5pgCFSHaDAodfgJ5cQ
it is listed at $379.
Newark's price is $449 and 60 days lead time.
These people seem to have a 15% discount currently.
http://www.metrictest.com/catalog/promotion/agilent_hhdmm.jsp
I suspect availability is a problem from any source.
In Google the search string
1253a meter
seemed to be fairly useful.
.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
An experiment.
These are the amp readings of a 1875W blow dryer on its highest setting.
These are the voltage readings under load
These are the voltage readings under no load.
The math doesn't seem to match either tester.
120? ? 1875=7.7 ohms
116V ? 7.7 =15A
105 ? 7.7=13.6A
These results surprise me, thought this would be easy.
These are the amp readings of a 1875W blow dryer on its highest setting.
These are the voltage readings under load
These are the voltage readings under no load.
The math doesn't seem to match either tester.
120? ? 1875=7.7 ohms
116V ? 7.7 =15A
105 ? 7.7=13.6A
These results surprise me, thought this would be easy.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090218-1953 EST
chris:
Your DC measurement on a 9 V battery showed a difference of about 3.1 % (1 - 9.3/9.6 = 0.031 --- Ideal to Greenlee).
Your original values from post 1 were Ideal to Greenlee 124.8 to 113.7 or about 10.7 % difference (124.8/112.7 = 1.107) and a reversal of which was larger when compared to DC.
Now in AC current it is 12.1 to 11.7 or about 3.4 % but opposite the DC voltage relative to the larger one.
Next another pair of AC voltage readings. 116.2 to 105.6 about 10 % difference correlating with your original AC voltage difference.
Because I would not expect two different locations to have low AC supply voltage I am going to guess that Greenlee has the major AC voltage problem.
It is likely that hair driers and heaters consume less power than their rating. Reasons for this might be for advertizing, and to prevent a 6 sigma unit going above the rating.
.
chris:
Your DC measurement on a 9 V battery showed a difference of about 3.1 % (1 - 9.3/9.6 = 0.031 --- Ideal to Greenlee).
Your original values from post 1 were Ideal to Greenlee 124.8 to 113.7 or about 10.7 % difference (124.8/112.7 = 1.107) and a reversal of which was larger when compared to DC.
Now in AC current it is 12.1 to 11.7 or about 3.4 % but opposite the DC voltage relative to the larger one.
Next another pair of AC voltage readings. 116.2 to 105.6 about 10 % difference correlating with your original AC voltage difference.
Because I would not expect two different locations to have low AC supply voltage I am going to guess that Greenlee has the major AC voltage problem.
It is likely that hair driers and heaters consume less power than their rating. Reasons for this might be for advertizing, and to prevent a 6 sigma unit going above the rating.
.
weressl
Esteemed Member
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090219-1054 EST
Here are measurements on an old hair drier rated at 1500 W that I use for drying PC boards and testing boards.
GR 1650A bridge 90 microhenrys, Q=0.02 at 1 kHz. DC resistance 15.4 ohms. At 120 V line current is about 8 A.
Calculated inductive reactance at 60 Hz is 0.03 ohms. Calculated power from 120 V and 15.4 ohms is 935 W. Calculated power from 120 V and 8 A is 960 W.
An Ungar 1000 W heat gun. 50 microhenrys at 1 kHz, 13.5 ohms DC resistance. Load current 7.5 A at 120 V.
None of these were high accuracy measurements, but the inductive reactance is so small it can be ignored. In particular the inductance is probably smaller because this is the end of the range for low Q on the bridge.
.
Here are measurements on an old hair drier rated at 1500 W that I use for drying PC boards and testing boards.
GR 1650A bridge 90 microhenrys, Q=0.02 at 1 kHz. DC resistance 15.4 ohms. At 120 V line current is about 8 A.
Calculated inductive reactance at 60 Hz is 0.03 ohms. Calculated power from 120 V and 15.4 ohms is 935 W. Calculated power from 120 V and 8 A is 960 W.
An Ungar 1000 W heat gun. 50 microhenrys at 1 kHz, 13.5 ohms DC resistance. Load current 7.5 A at 120 V.
None of these were high accuracy measurements, but the inductive reactance is so small it can be ignored. In particular the inductance is probably smaller because this is the end of the range for low Q on the bridge.
.
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