Decade [ Resistance/Capacitance ] Boxes - Repeat Accuracy Concern ?  - Page 1
Forum section: electronics / general

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 23, 2013, 02:26:42 pm
content: @ All,For My Planned Multimeter Reviews I Am Thinking Of Buying One Resistance And One Capacitance Decade Box .My Concern Is That Due To Dial And Switch Design I Would Be Getting Variable Outputs Where Accuracy Is Concerned .Is This Concern Correct Or Not Correct .Percentage Of Resistance Is Not a Issue The Repeat Accuracy Is ? . Can i Have Your Options Please .

author: Vgkid
author_rank: Super Contributor
timestamp: July 23, 2013, 10:00:13 pm
content: What level of accuracy are you looking at getting?nice resistance decades are much cheaper than the comparable precision capacitance decade boxes, even on the used market.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 24, 2013, 04:53:02 am
content: Quote from: Vgkid on July 23, 2013, 10:00:13 pmWell,There Has To Be a Contact Resistance In All Switches And Rotatory Dials .I Am Sure Every Time You Trigger/Detrigger It Varies

author: Vgkid
author_rank: Super Contributor
timestamp: July 24, 2013, 05:37:03 pm
content: you are correct, generally higher end resistance boxes have lower switch resistances, so this is not of always a concern. I have never used a high end capacitane box, so I can't really help you. But it should work the same way, luckilly you can most likely select a setting that would act as a fully open in order to correct for the stray capacitances in the cable, if the meter has that option.

author: AG6QR
author_rank: Frequent Contributor
timestamp: July 24, 2013, 06:12:12 pm
content: Quote from: Amarbir[Lynx-India] on July 23, 2013, 02:26:42 pmAre you really going to check all of the resistances the decade box is capable of generating? Or just spot check a few values at standardized intervals?For a multimeter review, I'd rather see a quality measurement of a handful of precisely and accurately known resistances, at various widely spaced values. In other words, check the measurement of a few discrete, stable parts. One way to do that is to buy something like the DMMCheck or DMMCheck Plus offered by voltagestandard.com .You could always buy the precision resistors directly from digi-key or your favorite supplier, but their initial resistance value has a tolerance that's typically quite a bit wider than their later drift. So it's nice to have that baseline measurement of the precise resistance by someone who has a calibrated instrument. This may not be absolutely required for checking performance of a low-precision handheld multimeter, though.With a decade resistance box, you've got the switch contact resistance to think of, and it's not only somewhat hard to characterize, but worse, it will change over time as the switch contacts oxidize and scrape against each other. It may change widely in a few seconds as you flip the switches back and forth, dislodging a bit of oxidization.I'm not nearly as familiar with techniques for precisely measuring capacitance, but I'd think a similar strategy would apply. Use a handful of discrete, stable, precision capacitors. Measure them with a good meter to establish a baseline. Then measure them with the meters under test.

author: mariush
author_rank: Super Contributor
timestamp: July 24, 2013, 06:44:56 pm
content: Well, my first opinion would be tostopcapitalizing everywordyoutypebecauseitdoesn'tmakeyousoundsmarteranditmakesyourmessageshardtoreadOtherwise, ag6qr is spot on.Unless you're going to spend a few hundred dollars, you're going to have a decade resistance box that has only 0.5% accuracy or something like that, to which you'll add the contact resistance and so on.You're better off with buying a few 0.01% resistors with much lower temperature coefficients which you could mount inside a box of some sort and control the temperature inside.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 24, 2013, 06:49:20 pm
content: QuoteCorrect ,Its Better Precision Resistances and Capacitors And Have Them Measured With a Baseline Instrument .Infact i Am Fully Geared For My Reviews I Have The Following1 : Protek Function Generator2 : DC Power Supply3 : Voltage Standard DMM Check Plus4 : Voltage standard Pentaref5 : A Chinese Voltage Ref Like Pentaref " That i Like Billion Times Better To Dougs Pentaref ".Damn This is just USD 24 Lol6 : Protek 50000 Multimeter For Some Reference7 : Planned Purchase Of Agilent U1253B8 : Planning To Buy a High End Bench Instrument Also9 : Brain And Support From You All

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 24, 2013, 06:52:24 pm
content: Quote from: mariush on July 24, 2013, 06:44:56 pmApologies ,This is The Way I Type "Seriously " .I Have Tried Zillion Times I Cannot Help It .Its Impossible For Me To Type Properly .My Thing is that i know the contact resistance would vary .Hence having a decade box is a utterly butterly wrong idea in the first place

author: mariush
author_rank: Super Contributor
timestamp: July 24, 2013, 08:12:32 pm
content: I understand that it may be something specific to your country or region and you may have been taught this way, but you're addressing to a worldwide audience so if you want the most results you should aim for the most viewer friendly way to write.If you wish to go the extra mile, feel free to paste your texts intohttp://www.convertcase.net/then click on your buttons below the text box to have your text corrected.