On Wed, 2 Sep 2020 17:11:28 +0100, Martin Brown <'''newspam'''@nonad.co.uk> wrote:>On 01/09/2020 16:48, Phil Hobbs wrote: >> On 2020-09-01 11:11, jlarkin@highlandsniptechnology.com wrote: >>> >>> >>> https://www.electronicdesign.com/technologies/test-measurement/whitepaper/21140081/warning-your-dmm-is-discharging-your-battery-cell?utm_source=EG+ED+Today&utm_medium=email&utm_campaign=CPS200828010&o_eid=7322A4702401H9R&rdx.ident%5Bpull%5D=omeda%7C7322A4702401H9R&oly_enc_id=7322A4702401H9R >>> >>> >>> It's sad how bad the electronics press has become. >> >> Good golly, Miss Molly, I'm sure glad he put in that table.� Ohm's law >> makes my head hurt. > >:-) Helps to use up more real estate in the article. > >We should go back to old school potentiometer measurements of voltage - >then no current flows at all when you have balanced the bridge.Galvos were slow and not very sensitive. A decent DVM will leak picoamps on a low voltage range, and not take 30 minutes of your time to make a measurement. I charged a 2.2u film cap to 5 volts and plugged that into my Fluke. I'll watch that for a while. There are cheap opamps with fA input currents.
typically stupid ED article
Started by ●September 1, 2020
Reply by ●September 2, 20202020-09-02
Reply by ●September 2, 20202020-09-02
On 09/02/20 17:33, Tom Gardner wrote:> On 02/09/20 17:11, Martin Brown wrote: >> On 01/09/2020 16:48, Phil Hobbs wrote: >>> On 2020-09-01 11:11, jlarkin@highlandsniptechnology.com wrote: >>>> >>>> >>>> https://www.electronicdesign.com/technologies/test-measurement/whitepaper/21140081/warning-your-dmm-is-discharging-your-battery-cell?utm_source=EG+ED+Today&utm_medium=email&utm_campaign=CPS200828010&o_eid=7322A4702401H9R&rdx.ident%5Bpull%5D=omeda%7C7322A4702401H9R&oly_enc_id=7322A4702401H9R >>>> >>>> >>>> It's sad how bad the electronics press has become. >>> >>> Good golly, Miss Molly, I'm sure glad he put in that table. Ohm's >>> law makes my head hurt. >> >> :-) Helps to use up more real estate in the article. >> >> We should go back to old school potentiometer measurements of voltage >> - then no current flows at all when you have balanced the bridge. > > Literally, in my case. NiFe + Weston cell + metre rule + resistance wire. > Ah, them's were the days. > > >> If he was complaining about the load that a Model 7 Avo puts on the >> battery under test which ISTR was 500R/volt then he might have a >> point. They were virtually indestructible though. I still have a >> mostly working one. The ohm's range is shot but current and voltage >> are fine. > > I remember a story told at GPO/BT Martlesham Labs. > > They had an Avo salesman and a (newfangled) DMM salesman demonstrate > the virtues of their equipment. It was neck-and-neck at the end of > the formal evaluation. > > Then the DMM salesman threw the DMM across the room, walked over and > picked it up, and made another measurement. > > I don't know whether or not he was grinning.Drop an AVO once and the plastic movement frame breaks. The General Electric (uk) was a much better meter imho. AVO 8's looked obsolete by the 1970s and the cramped scale was a pain... Chris
Reply by ●September 2, 20202020-09-02
On Tue, 01 Sep 2020 17:38:46 -0700, John Larkin <jlarkin@highland_atwork_technology.com> wrote: [snip]> >We did a few products using a Zynq, with dual-core 600 MHz ARM CPUs, >running the Linux that comes with the Xilinx tools. Just a little >futzing with priorities got a critical task to run with worst-case >timeouts in the ballpark of 20 us. > >"Any OS is an RTOS if it's fast enough."Well, no. Realtime does not mean really fast, it means the the latency to do <long list> is *predictable* and short enough for the task at hand, so you can draw timeline that will be followed well enough. As discussed earlier, by favorite example is a rotary cement kiln. I lived through the days of the Hard RT versus Soft RT wars, and the problem was that in systems of any size, hard RT was too fragile to live. So, we would partition the system into domains. The largest was non-RT, a smaller part was soft RT (VxWorks), and a very small parte was hard RT (now often done in FPGAs). Joe Gwinn
Reply by ●September 2, 20202020-09-02
On Wed, 02 Sep 2020 11:24:20 -0700, John Larkin <jlarkin@highland_atwork_technology.com> wrote:>On Wed, 2 Sep 2020 17:11:28 +0100, Martin Brown ><'''newspam'''@nonad.co.uk> wrote: > >>On 01/09/2020 16:48, Phil Hobbs wrote: >>> On 2020-09-01 11:11, jlarkin@highlandsniptechnology.com wrote: >>>> >>>> >>>> https://www.electronicdesign.com/technologies/test-measurement/whitepaper/21140081/warning-your-dmm-is-discharging-your-battery-cell?utm_source=EG+ED+Today&utm_medium=email&utm_campaign=CPS200828010&o_eid=7322A4702401H9R&rdx.ident%5Bpull%5D=omeda%7C7322A4702401H9R&oly_enc_id=7322A4702401H9R >>>> >>>> >>>> It's sad how bad the electronics press has become. >>> >>> Good golly, Miss Molly, I'm sure glad he put in that table.� Ohm's law >>> makes my head hurt. >> >>:-) Helps to use up more real estate in the article. >> >>We should go back to old school potentiometer measurements of voltage - >>then no current flows at all when you have balanced the bridge. > >Galvos were slow and not very sensitive. A decent DVM will leak >picoamps on a low voltage range, and not take 30 minutes of your time >to make a measurement. > >I charged a 2.2u film cap to 5 volts and plugged that into my Fluke. >I'll watch that for a while.So far, the voltage is increasing. Looks like about 10 pA equivalent. -- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Reply by ●September 4, 20202020-09-04
On 2020-09-02 12:11, Martin Brown wrote:> On 01/09/2020 16:48, Phil Hobbs wrote: >> On 2020-09-01 11:11, jlarkin@highlandsniptechnology.com wrote: >>> >>> >>> https://www.electronicdesign.com/technologies/test-measurement/whitepaper/21140081/warning-your-dmm-is-discharging-your-battery-cell?utm_source=EG+ED+Today&utm_medium=email&utm_campaign=CPS200828010&o_eid=7322A4702401H9R&rdx.ident%5Bpull%5D=omeda%7C7322A4702401H9R&oly_enc_id=7322A4702401H9R >>> >>> >>> It's sad how bad the electronics press has become. >> >> Good golly, Miss Molly, I'm sure glad he put in that table. Ohm's law >> makes my head hurt. > > :-) Helps to use up more real estate in the article. > > We should go back to old school potentiometer measurements of voltage - > then no current flows at all when you have balanced the bridge. > > I am a bit surprised they use a 10M shunt though. Reliable precision > 100M and 1G resistors are relatively common and have been for ages. > >> The guy works at _Keysight_. "How are the mighty fallen." Or maybe >> it's their customers. > > Formerly Agilent, formerly HP - do they change company name each time > there is a body to be buried?Every time they want to hive off their test equipment business in favour of the Junk of the Month--first it was computers and printers, then biomed instruments. (They ruined their computer and printer business--I've no idea whether the biomed stuff is still any good.)> If he was complaining about the load that a Model 7 Avo puts on the > battery under test which ISTR was 500R/volt then he might have a point. > They were virtually indestructible though. I still have a mostly working > one. The ohm's range is shot but current and voltage are fine.I have a beautiful Model 8 Mk IV that came from the collection of a guy who also collected Rolls-Royces. It's in perfect condition and has not a trace of stickiness in the meter movement. That one was the best of the classical Universal Avometers. I also had a Model 16 that was more modern-looking but was not in the same class at all. You had to thump it every time you wanted to make a measurement, like a cheap barometer. I eventually tossed it. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●September 4, 20202020-09-04
On 2020-09-02 11:00, Steve Wilson wrote:> jlarkin@highlandsniptechnology.com wrote: > >> On Wed, 2 Sep 2020 07:36:28 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> Another Tap on the voltage divider. >>>>> Even a 10M input, $20 DVM is a decent picoammeter. > > Assuming 200 mV on the lowest scale, I get 20 nanoamperes full scale. >Which at 4.5 digits gets you 1 pA per count. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●September 4, 20202020-09-04
On Fri, 4 Sep 2020 09:38:52 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2020-09-02 12:11, Martin Brown wrote: >> On 01/09/2020 16:48, Phil Hobbs wrote: >>> On 2020-09-01 11:11, jlarkin@highlandsniptechnology.com wrote: >>>> >>>> >>>> https://www.electronicdesign.com/technologies/test-measurement/whitepaper/21140081/warning-your-dmm-is-discharging-your-battery-cell?utm_source=EG+ED+Today&utm_medium=email&utm_campaign=CPS200828010&o_eid=7322A4702401H9R&rdx.ident%5Bpull%5D=omeda%7C7322A4702401H9R&oly_enc_id=7322A4702401H9R >>>> >>>> >>>> It's sad how bad the electronics press has become. >>> >>> Good golly, Miss Molly, I'm sure glad he put in that table.� Ohm's law >>> makes my head hurt. >> >> :-) Helps to use up more real estate in the article. >> >> We should go back to old school potentiometer measurements of voltage - >> then no current flows at all when you have balanced the bridge. >> >> I am a bit surprised they use a 10M shunt though. Reliable precision >> 100M and 1G resistors are relatively common and have been for ages. >> >>> The guy works at _Keysight_.� "How are the mighty fallen."� Or maybe >>> it's their customers. >> >> Formerly Agilent, formerly HP - do they change company name each time >> there is a body to be buried? > >Every time they want to hive off their test equipment business in favour >of the Junk of the Month--first it was computers and printers, then >biomed instruments. (They ruined their computer and printer >business--I've no idea whether the biomed stuff is still any good.)Agilent bought Varian and promptly killed the NMR and FTMS groups, who were my best customers at the time.> >> If he was complaining about the load that a Model 7 Avo puts on the >> battery under test which ISTR was 500R/volt then he might have a point. >> They were virtually indestructible though. I still have a mostly working >> one. The ohm's range is shot but current and voltage are fine. > >I have a beautiful Model 8 Mk IV that came from the collection of a guy >who also collected Rolls-Royces. It's in perfect condition and has not >a trace of stickiness in the meter movement. That one was the best of >the classical Universal Avometers. I also had a Model 16 that was more >modern-looking but was not in the same class at all. You had to thump >it every time you wanted to make a measurement, like a cheap barometer. >I eventually tossed it.My Fluke 8845 seems to output +10 or 15 pA on the 10 volt range. -- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Reply by ●September 4, 20202020-09-04
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> On 2020-09-02 11:00, Steve Wilson wrote: >> jlarkin@highlandsniptechnology.com wrote: >> >>> On Wed, 2 Sep 2020 07:36:28 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> Another Tap on the voltage divider. >>>> > >>> Even a 10M input, $20 DVM is a decent picoammeter. >> >> Assuming 200 mV on the lowest scale, I get 20 nanoamperes full scale. >> > > Which at 4.5 digits gets you 1 pA per count. > > Cheers > > Phil HobbsAs with most instruments, probably should not use DVMs below 10% of full scale. That works out to 2nA. Got to find a more sensitive DVM with higher input impedance. I recall that some switch out the divider on the lowest range and use the impedance of the input stage for measuring current. An old Fluke DVM did this, and changed the scale to read in nanoSiemens, which was pretty impressive at the time.
Reply by ●September 4, 20202020-09-04
Steve Wilson <spam@me.com> wrote:> Got to find a more sensitive DVM with higher input impedance. I recall > that some switch out the divider on the lowest range and use the > impedance of the input stage for measuring current. An old Fluke DVM did > this, and changed the scale to read in nanoSiemens, which was pretty > impressive at the time.The DVM was the Fluke 8020A. Here's the datasheet: https://stevenjohnson.com/pics/fluke-8020a-op-guide.gif
Reply by ●September 4, 20202020-09-04
On 09/04/20 23:08, Steve Wilson wrote:> Steve Wilson<spam@me.com> wrote: > >> Got to find a more sensitive DVM with higher input impedance. I recall >> that some switch out the divider on the lowest range and use the >> impedance of the input stage for measuring current. An old Fluke DVM did >> this, and changed the scale to read in nanoSiemens, which was pretty >> impressive at the time. > > The DVM was the Fluke 8020A. Here's the datasheet: > > https://stevenjohnson.com/pics/fluke-8020a-op-guide.gif >Still have one of the Fluke 80-xx series and use it regularly. Handy size for the bench and just refuses to die. 5 ukp at a car boot decades aga... Chris
