FLUKE 8845A / 8846A with 7.5 digits resolution? - Page 1
Forum section: electronics / testgear

author: Arielo
author_rank: Newbie
timestamp: January 25, 2019, 04:44:59 pm
content: Hi everyone, I've bought (well, my company bought one, but it's in my office, and only I use it), a new (as in "not used", because the model is quite old now) Fluke 8845A multimeter.Now, I've no real need for such a high precision multimeter, but we bought one anyway, about 6 month ago.I was playing with it the other day, it came with an USB to RS232 cable, witch I used to connect it to a computer, and I've read the programmers manual to try and get a reading out of it, just for fun.I've set it in remote (SYST:REM), and then I used the command "READ?" to get a reading (it's NOT case sensitive, you can write the commands without using capital letters), the result comes with 1 digit, a decimal point, 6 trailing digits (actually, 8, but the las 2 are ALWAYS zero), and then the E (x10^ ) and the exponential. It doesn't round it to make it an engineering number (E in multiples of 3), but the intesting thing is that it looks like it comes with an extra digit as a bonus.For example, I connected the Fluke input to my lab power supply (OWON ODP6033, again, I'm not in need of high accuracy and precision, but this power supply comes with 2 channels of 60Vx3A each, and that was actually quite useful for me, but this has nothing to do with the Fluke, sorry, I sidetracked). So, I set the output to 1V, and when I issue a reading with the serial command, the Fluke displays 0.998037, and the serial port returns the value +9.98036900E-01, and as you can see, the las digit of the multimeter display is the rounded result of the last 2 digits I get on the serial port. If I set the output to 9volts, the multimeter displays +8.99642, but the serial port returns +8.99642400E+00, again, an extra digit of resolution.Now, I don't have any means to test the accuracy of the Fluke (I'm shure it's spot on, even though that by the time I purchased the unit it had 10 month since it was calibrated), but would this mean that the multimeter is actually a 7.5 digits with 0.0035% accuracy? (the accuracy is on the specs for the 6.5 digits specified, I'm not shure if it would translate exactly like that to a 7.5 digits readout through the serial port).I couldn't find any information online, so I came here looking for answers, but I coudn't find any post that somebody tried reading the meassurement via a serial command.I hope that somebody reads this and tries it out.I personally think it would be cool if Dave reads this and makes a video testing this thing, and maybe testing other 6.5 digits multimeters to see if they offer the same 7.5 digits via the serial commands, and compares the readings with an actual 7..5 digits (or 8.5 digits) multimeter.Greetings from Argentina,Ariel

author: Mr. Scram
author_rank: Super Contributor
timestamp: January 25, 2019, 05:05:13 pm
content: Many meters do something similar. I think what you're seeing is a direct readout of a single internal reading. To get to the value that's within specifications and presented to you during normal operation of the device, the device integrates or averages more than one reading to eliminate things like noise. I'd treat the extra digit as is, and not as an extra full digit.

author: TiN
author_rank: Super Contributor
timestamp: January 25, 2019, 05:43:44 pm
content: Extra digit is just the noise, and does not carry any useful information.