Fluke 28II  Problem displaying Frequensy on 10A ACI  - Page 1
Forum section: electronics / general

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: August 19, 2011, 01:41:12 am
content: The last 20 days I did some testing and comparisons, by using the Fluke 28II as dedicated ammeter on AC Mains,operating - measuring ACI continuously for 20 days.The load are three pulsing PSU ( three battery chargers + one small refrigerator ).The load of this line goes from 400mA AC to 950mA max.The Fluke 28II was connected as ammeter and was capable to display the 50Hz Mains frequency when is set at the Auto range minimum 6A range,when I use manual range AC 10A , the 28II is unable to display the Mains frequency and shows 00Hz.By reading the manual there is some generic talk about triggering levels and sensitivity.The problem by my point of view, are that even one load close to 1A AC (220VA), looks incapable to trigger the DMM frequency counter.As long the User's manual does not define the minimum amount of the needed current so to trigger the frequency counter at the 10A range,I am forced to ask publicly, and seek for one reliable answer about this issue.Yes I did similar tests by using the Agilent U1272A, and the DMM managed to operate and indicate the frequency at both ranges of it, like 3A and 10A ACI with a minimum of load of 400mA or less.I think that the 28II activates by it self the LPF (filter by default at ACI ), and so I activated too the LPF manually at the Agilent DMM,so the comparison to be apples with apples.I am open to questions if there is any.

author: Unknown
author_rank: Unknown
timestamp: August 19, 2011, 04:38:32 pm
content: See table 7, page 30 of the English user manual. Trigger level for the 10A AC range is 3A. Not sure why it's not mentioned in the detailed specifications.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: August 19, 2011, 06:31:30 pm
content: Hmm, I did spot it ..But I am not happy about it.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 19, 2011, 09:04:45 pm
content: Why are you upset that it works properly unless you manually set the wrong range? Low trigger thresholds are bad as it increases the likelihood of false triggers and incorrect readings. As long as it works on auto-ranging and works when you set the range correctly, why do you care?

author: Unknown
author_rank: Unknown
timestamp: August 19, 2011, 10:41:00 pm
content: Quote from: ejeffrey on August 19, 2011, 09:04:45 pmIt's part of an ongoing vendetta against Fluke. It serves no purpose and it's far from good or clever engineering. The equivalent of complaining that the BMW M3 fails to match it's published 0-100 times when launched in a high gear.I guess the Agilent U1272A should equally be condemned because it fails to reliably measure resistance when set to any of its current ranges. Though some would say that is just being negative.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: August 19, 2011, 11:12:37 pm
content: Quote from: ejeffrey on August 19, 2011, 09:04:45 pmYou are theoretically correct.But behind this post is one long story ( investigation ), that accidentally started when I pulled one line of the three phases from my mains electrical board so to be able to connect any DMM of the two, so to be tested as ammeters in line, plus to test my AC/DC clamp.The ACI load was no significant , but the unexpected was that those three chargers with pulsing PSU, when they was activating the charging mode , they was look like three drums that caused three asynchronous strong pulses per second.Those pulses was creating such amount of interference, that the frequency counter of the U1272A was unable to read the 50Hz frequency.The Fluke 28II it was able at the auto-range , and because of that I did the Agilent company upside-down.After of two weeks investigation, I got the reply from their highest in rank technical engineer, that I have to activate the Low pass Filter on the DMM , and if there is strong interference , I had to manually move at the 10A range , because the filter becomes ever more powerful.The LPF on the ACI on the specific DMM does not engage automatically as the Fluke 28II does,and so by activating it solved the half of the problem.The half of the problem is the first stage of this "application", that all those three chargers ( loaded with batteries),they just check the condition of the batteries before they start the "true " charge .At those 5-7 first minutes, the amount of the interference is lower .And both, the Agilent and the Fluke DMM was able to handle the interference, and by their Low Pass filters activated,they both show the 50HZ .When the chargers started the true charging mode = highest interference level, the Agilent come close to show some instability at displaying the frequency of 50HZ ( like a tiny play up) 50-49-51-50Hz .And the Fluke started to have real problems and gave readings like 50 - 75- 80- 50 - 75- 80- 50 Hz = unstable behavior.By following the suggestion of the Agilent technical department, that was to manually select the 10A range,the U1272A it did lock it self at the 50Hz = the Low Pass Filter of it, it did a beautiful job.The Fluke failed to display frequency at the 10A range , and failed to maintain the reading of 50Hz at the highest interference level,that those chargers could produce.By all those happenings, and my investigation, I learned allot of those details,and this is the synopsis.1)The Fluke 28II and probably and the 87V, they have as selection the use of the LPF for the ACV,but they activate the LPF by default at the ACI,with out the LPF indicator to become active.2)The Agilent U1272A offers the same choice about the LPF on ACV,but it does not do ACI by LPF by default, you have to enable it in the main options.If you do that, every time that you activate ACI the filter gets active too.And theLPF indicator becomes active on the screen.3)On low current troubleshooting with lots of pulses and interference, the Fluke fails to perform,as the Agilent unit does.I wrote 11 pages review about the Agilent U1272A and I wrote that I was unable to test the Low Pass filter,because I do not have access at any variable speed motor systems ( pulses and spikes).And the pulses and the interference was hidden in those tiny PSU of those three chargers.From today I can tell, that I do know those two DMM models " Fluke 28II & Agilent U1272A ", better that my own palm.Speaking about weakness and strong points.After all this explanations I am not upset any moreBut I do not know how they feel in the Fluke camp.

author: 500in1
author_rank: Contributor
timestamp: August 20, 2011, 01:40:40 am
content: Quote from: Kiriakos-GR on August 19, 2011, 11:12:37 pmAre you saying that the Fluke worked (highlighted in green) but the Agilent was not set up properly the first time you measured, and after contacting Agilent you tried measuring again but this time you used the Fluke in manual to match Agilent's setting? I may be wrong but this is how I interpreted your posting.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: August 20, 2011, 02:12:35 am
content: Quote from: 500in1 on August 20, 2011, 01:40:40 amCorrect ..Quote from: 500in1 on August 20, 2011, 01:40:40 amCorrect ..Due the fact that it came to the point to become unstable at maintaining a stable frequency reading at the 6A (minimum range).I was unaware at that time about the triggering limitation of the Fluke.The Fluke does 6A & 10AThe Agilent one does 3A & 10ASomeone he would expect that the Fluke at 6A it would do an even better job, than the Agilent at 3A range.At list if those Low Pass filters was build equally.And those are the pictures that I had send to Agilent.