Microvolt reading  makeup? - Page 1
Forum section: electronics / projects

author: tyreman
author_rank: Newbie
timestamp: May 11, 2010, 01:42:58 pm
content: If you have a meter that won't read microvolts but only miilliampsIs it possible to make up a adaptor or place a component in line with the test lead to read microvolts off the meter while on the DC volts meter position?the dc volts would then be read as microvolts

author: Unknown
author_rank: Unknown
timestamp: May 11, 2010, 02:36:51 pm
content: It's called an amplifier. Dave's ucurrent is basically a microvoltmeter (not sure about actual resolution) with some switchable shunt resistors, so that would be one example.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: May 11, 2010, 04:42:37 pm
content: Quote from: tyreman on May 11, 2010, 01:42:58 pmHow low you need to get ?

author: Simon
author_rank: Unknown
timestamp: May 11, 2010, 08:39:12 pm
content: you need to amplify your microvolts to mV and read them with your meter, the only issue is offset voltages, op amps are the obvious solution but unless you have 1-2 uV offset your readings will be very far out, I think multiple stages of amplification will help

author: Unknown
author_rank: Unknown
timestamp: May 11, 2010, 11:13:19 pm
content: How will multiple stages help, I think the next stage will just amplify the offset of the previous one and add some extra? Isn't offset mainly dependent on small differences in the semiconductor process and temperature?I'd just go for an auto-zero op-amp like Dave did. A cheap way might be to try to trim (some of) the offset out, but you will have to adjust it if the temperature of the op-amp changes (which is basically a manual version of an auto-zero op-amp). Both Dave's video about the design of the ucurrent and his explanation of the auto-zero/chopper op-amp (this was an early one) would be helpful if you decide to go this route.At 1uV, you will probably notice thermocouple effects and other fun stuff. Keithley has a 'Low level measurements handbook' that can be downloaded for free from their website. 1uV is on the upper side of what they consider 'low-level'. It contains lots of useful information, I have a hardcopy version that they send to me for some reason (not that I mind).Another way would be to use a precision DMM, but this is definitely the more expensive route (between $25 and $250 or so). For example, the HP 3468A/3478A (about $50 to $150) has a resolution of 1uV at the 300mV range (but this is the limit, so if you actually want to measure 1uV with any accuracy, you need better). Keithley has a DMM in the 17x series that they call microvolt DMM, these can sometimes found cheaply on ebay, it also has a resolution of 1uV.

author: Pyr0Beast
author_rank: Contributor
timestamp: May 12, 2010, 05:00:11 am
content: Well, you also need good probes for that. In ranges of uV even small stray voltages add up.

author: personalinformatics
author_rank: Newbie
timestamp: May 15, 2010, 04:37:31 pm
content: The datasheet for Linear Technology's LT1150 has an application section for "ACHIEVING PICOAMPERE/MICROVOLT PERFORMANCE"http://cds.linear.com/docs/Datasheet/1150fb.pdfUser manual for HP Nanovoltmer see "Chapter 7: Measurement Techniques and Sources of Error"http://instructor.physics.lsa.umich.edu/adv-labs/Tools_Resources/HP%2034420A%20user's%20guide.pdf