Programmable 0.01% DC source? - Page 1
Forum section: electronics / testgear

author: nctnico
author_rank: Super Contributor
timestamp: February 02, 2016, 11:45:11 pm
content: I'm looking for a device which outputs a DC voltage with (preferably) 0.01% or better accuracy and preferably programmable. I looked on Ebay but can't find something I really like. Any hints on where to look? I can spend a couple of hundred on it.

author: michaeliv
author_rank: Frequent Contributor
timestamp: February 02, 2016, 11:56:38 pm
content: How about :http://www.ebay.com/itm/Used-Agilent-Keysight-E3640A-30W-DC-Power-Supply-8V-3A-20V-1-5A-/381469490673http://www.ebay.com/itm/HP-66311B-0-15V-0-3A-5A-Peak-Mobile-Communications-DC-Source-Supply-Agilent-/151964937975

author: nidlaX
author_rank: Frequent Contributor
timestamp: February 03, 2016, 12:00:05 am
content: What range of outputs do you need at what power?

author: pelule
author_rank: Frequent Contributor
timestamp: February 03, 2016, 12:32:08 am
content: QuoteI can't recommend these tools for the requested 0.01% accuracy. They are internally based on a 12 bit DAC, means an error > 0.025%, not having taken other errors sources (like drift, part tolerances) into account.One option, thus not a cheap one, is the HP 3245A programmable sourcehttps://www.eevblog.com/forum/repair/repair-hp-something/msg851723/#msg851723.

author: michaeliv
author_rank: Frequent Contributor
timestamp: February 03, 2016, 12:51:54 am
content: Quote from: pelule on February 03, 2016, 12:32:08 amIndeed they are both 0.05%. It's difficult to find 0.01% at ~$200.

author: nidlaX
author_rank: Frequent Contributor
timestamp: February 03, 2016, 01:44:29 am
content: Quote from: michaeliv on February 03, 2016, 12:51:54 amDepends on the range and power requirements. You can find 0.02 - 0.01% class calibrators on eBay under $200 almost every week.

author: Tim F
author_rank: Regular Contributor
timestamp: February 03, 2016, 01:48:40 am
content: Tbh you are probably best off making your own with that budget. Measure a stable voltage reference to <0.01% with a 6 1/2 digit multimeter and hook that up to a decent DAC like an LTC2400.As far as buying something new, this is probably the best bang for buck:http://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-detail

author: billfernandez
author_rank: Regular Contributor
timestamp: February 03, 2016, 07:39:30 am
content: If your primary need is simply to have a very accurate voltage reference, and if 5V or 10V will do, you can get a 0.003% or better voltage standard for about $50 fromhttp://www.voltagestandard.com

author: michaeliv
author_rank: Frequent Contributor
timestamp: February 03, 2016, 08:03:28 am
content: Somewhat unrelated: I've wondered about this listing-http://www.ebay.com/itm/-/251756273626- How they can claim +-2ppm initial accuracy since they claim to null it to a Fluke 732A (calibrated once per year I understand) which itself is +-6ppm.- How is the nulling done ? Wouldn't that introduce additional error due to offset errors ?- They mention: "monitoring the calibration on an Agilent 3458A 8-1/2 digit multimeter" ... Why would this be necessary, that is +- 8ppm, less precise than the Fluke.- The manufacturer claims drift of +-5ppm / 1000hr for the voltage reference after stabilization, how can they claim less than 1ppm / 3000hr ?

author: Tim F
author_rank: Regular Contributor
timestamp: February 03, 2016, 08:24:39 am
content: Quote from: michaeliv on February 03, 2016, 08:03:28 amSeehttps://www.eevblog.com/forum/metrology/calibratory-d-105-dc-precision-voltage-reference-standard/Claimed specs aside, the dodgy construction is probably reason enough not to buy one.

author: nctnico
author_rank: Super Contributor
timestamp: February 03, 2016, 11:42:30 am
content: Quote from: pelule on February 03, 2016, 12:32:08 amI have been looking at the HP3245A programmable sources and I also found the Fluke 4210A programmable sources. The HP3245A is overprized for it's age (they are from the early 90's!) and the Fluke 4210A has a complex adjustment sequence. Ideally I'd like the source to be calibrated as well. And then there is the DIY versus buy dillemma. There is no shortage of 'cheap' 0.01% accuracy voltage references and together with a good DAC they could be turned into a programmable source as well. If the source can output 50mA it will be more than fine.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: February 03, 2016, 12:01:13 pm
content: Quote from: nctnico on February 02, 2016, 11:45:11 pmGet the EVAL-AD5791SDZ AD evaluation board from Farnell (#2072467), add a good reference - LM399 (#2295479 from Farnell) will do nicely, however the board contains the layout for LTZ1000 (with some critical errors in the wiring though) and calibrate the lot with a good 6.5digits meter. If you need something to control the DAC over USB, you can get a processor board from AD (Farnell #1897089). The stability of this combination would easily be better than 50ppm (0.005%) in a reasonable lab temperature range and the DAC would allow you to set the voltage with 1ppm steps.CheersAlex

author: HKJ
author_rank: Super Contributor
timestamp: February 03, 2016, 01:54:52 pm
content: You can get one from here:http://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-detail

author: generic_username
author_rank: Regular Contributor
timestamp: February 03, 2016, 03:04:51 pm
content: So I got myself an Agilent E3633A used on Ebay 2 weeks ago and it was horrible out of cal: set 5.000V measured 5.100V with 2 different meters.What first comes to mind: Do you have a meter that has the accuracy for you to callibrate that yourself?

author: Kalvin
author_rank: Super Contributor
timestamp: February 03, 2016, 03:15:04 pm
content: For the DIYers:"20-Bit, Low-Power Digital-to-Analog Converter"http://www.ti.com/lit/ds/symlink/dac1220.pdfQuite inexpensive 20-bit DAC and could be usable in this project."A Standards Lab Grade 20-Bit DAC with 0.1ppm/°C Drift"http://cds.linear.com/docs/en/application-note/an86f.pdfThe design uses two 16-bit DACs."The 20-Bit DAC Is the Easiest Part of a 1-ppm-Accurate Precision Voltage Source"http://www.analog.com/library/analogdialogue/archives/44-04/AD5791.pdfUses a 20-bit DAC.

author: nctnico
author_rank: Super Contributor
timestamp: February 03, 2016, 03:30:19 pm
content: Quote from: generic_username on February 03, 2016, 03:04:51 pmAt the moment not. I see I have two options: get a calibrated DMM which can be used to calibrate a reference or get a reference which I can get calibrated/adjusted. The latter more or less rules out the DIY references from Ebay -with all due respect-.

author: TiN
author_rank: Super Contributor
timestamp: February 03, 2016, 04:28:32 pm
content: If you talking few fixed levels, you can get those chinese-made AD584/58X modules, which come with measured value.While it's a gamble, usually they are within 0.01%.What is this all for anyway? Maybe you can approach your problem from different angle?

author: nctnico
author_rank: Super Contributor
timestamp: February 03, 2016, 05:47:04 pm
content: Quote from: TiN on February 03, 2016, 04:28:32 pmI have to make a design which can measure voltages (0..10V) and currents (0..10mA) with reasonable accuracy and more importantly stability since most measurements will be relative. I'll also need to test small production runs and I'll like to do that automated. What I need is an accurate & stable reference (either voltage source or DMM) to check the prototype and preferably a voltage source to test the production units.

author: pelule
author_rank: Frequent Contributor
timestamp: February 03, 2016, 08:11:54 pm
content: Quote@ michaeliv - have a look to the thread discussing that all in detail...

author: pelule
author_rank: Frequent Contributor
timestamp: February 03, 2016, 08:31:44 pm
content: QuoteThat makes it more clear. You need- a DMM able to measure within required spec and an interface to control/read- a by an interface programmable voltage/current source with required stability (accuracy not important, will be corrected out)- a PC/Laptop with the same interface to control all three- a control software o control automatically (and optional logging the process)The PC/software sets desired output at the source (by measuring the exact value with the DMM) - a closed loop value setting.May be reasonable at your price target, if you are able to write the software yourself and you don't need a certified calibration.BRPeLuLe

author: michaeliv
author_rank: Frequent Contributor
timestamp: February 03, 2016, 09:57:20 pm
content: Quote from: Tim F on February 03, 2016, 08:24:39 amQuote from: pelule on February 03, 2016, 08:11:54 pmThanks, I did not know that there was already a thread about this.

author: TiN
author_rank: Super Contributor
timestamp: February 04, 2016, 02:51:16 am
content: Perhaps something like TI ADS1262 with good input voltage 4:1 divider and current shunt for 20mA range would fit your accuracy specs. It's TSSOP package (easy to solder), with rather stable reference and internal temp sensor. I wrote areviewof TI's PDK demo kit with this ADS and did some tests.As source you can use suitable DAC, referenced to same ADC's 2.5V reference. After you get measurement system calibrated, it would be matter of software to program DAC for specific values.Interface is SPI, which can be used with some MCU or even Raspberry Pi with ease.Of course you will need access to calibrated 5.5/6.5-digit DMM to get initial accuracy set. You can even loan DMM to do testing and calibrated and return it after, maybe.

author: dadler
author_rank: Unknown
timestamp: February 04, 2016, 09:51:40 pm
content: I managed to pick up an Advantest R6144 on eBay for about this price, just about matches your accuracy requirements.

author: nctnico
author_rank: Super Contributor
timestamp: February 08, 2016, 03:53:34 pm
content: I decided to buy a Keysight 34461A 6.5 digit DMM to at least be able to verify the circuit's own reference and perhaps do some automated calibration.

author: Someone
author_rank: Super Contributor
timestamp: February 09, 2016, 03:19:44 am
content: Quote from: michaeliv on February 03, 2016, 12:51:54 amEven big dollar SMUs don't have a 0.01% specification, at that level you rely on calibrated references.

author: generic_username
author_rank: Regular Contributor
timestamp: February 09, 2016, 07:01:02 am
content: Quote from: Someone on February 09, 2016, 03:19:44 amStupid question what's a SMU??

author: HKJ
author_rank: Super Contributor
timestamp: February 09, 2016, 07:15:33 am
content: Quote from: generic_username on February 09, 2016, 07:01:02 amSource Measure Unit, like a Keithley 2450:http://www.tek.com/keithley-source-measure-units/smu-2450-60-graphical-sourcemeterA four quadrant power supply (Source and sink, both positive and negative values) build together with a precision DMM.

author: generic_username
author_rank: Regular Contributor
timestamp: February 09, 2016, 09:06:26 am
content: thank you

author: nctnico
author_rank: Super Contributor
timestamp: February 09, 2016, 11:16:02 am
content: Quote from: Someone on February 09, 2016, 03:19:44 amThere is some equipment out there which can do 0.01% while being programmable. The HP/Agilent communications DC sources are not among such equipment. They claim 0.05% but they also have a lot of noise (1mV) at their outputs.

author: rfbroadband
author_rank: Unknown
timestamp: April 01, 2016, 05:53:12 pm
content: Keithley offers a so called "Precision, Low Noise DC Power Supply" 2280Shttp://www.tek.com/dc-power-supply/series-2280-precision-measurement-dc-power-suppliesbuilt in 6.5 digit DMMsource setting resolution 1mV, accuracy 0.02% + 3mVof course somewhat expensive...~2k$

author: HKJ
author_rank: Super Contributor
timestamp: April 01, 2016, 06:04:14 pm
content: Quote from: rfbroadband on April 01, 2016, 05:53:12 pmI love mine, but it will never replace one of my SMU's. They have different purpose and the SMU's are much more advanced.For a power supply I would select the 2280S, but for a reference I prefer the 2450. The 2450 do also have much better programming features than the 2280S.

author: nctnico
author_rank: Super Contributor
timestamp: April 01, 2016, 06:08:47 pm
content: The 2280S is interesting but in the end I bought a Keysight 34465A DMM and a 66311B DC telecom power supply. The 66311B seems to be stable within 100uV which is within the 0.01% mark for output voltages over 1V.

author: rfbroadband
author_rank: Unknown
timestamp: April 01, 2016, 09:56:44 pm
content: I hope the 66311 works out for you. The spec claims programming accuracy of 10mV with ripple/noise of 1mVrms (2280S is 1mV accuracy and 1mVrms ripple and noise).

author: nctnico
author_rank: Super Contributor
timestamp: April 01, 2016, 10:31:34 pm
content: Yes, the interesting thing about the 66311B is that the 0.05% spec is more likely to be driven by the DAC step size and load regulation than the (no-load) stability.

author: rfbroadband
author_rank: Unknown
timestamp: April 01, 2016, 11:35:07 pm
content: if you find out anything worth mentioning over the next few weeks (using this unit) in regards to the specs we discussed, please share a few of your observations. Thanks!

author: nctnico
author_rank: Super Contributor
timestamp: April 01, 2016, 11:52:53 pm
content: I posted some measurements here:https://www.eevblog.com/forum/testgear/my-poor-mans-smu-the-agilent-66311b/msg887016/#msg887016I also examined the reference but IMHO there is no use to put a better reference in the 66311B.

author: amspire
author_rank: Super Contributor
timestamp: April 01, 2016, 11:55:58 pm
content: There is also PWM. I had a discussion with A Hellene in 2012, and I did some tests. With a simple Arduino-type ATmega328P processor, a buffer IC attached to a 5V reference, a few resistors and capacitors, I was getting a stable D/A with 0.001% linearity and better then 1ppm resolution. The most expensive part is a decent reference IC.https://www.eevblog.com/forum/projects/general-purpose-power-supply-design-7488/msg106218/#msg106218Earlier in the thread, I did post the code. What I found was the jitter in the Atmega (set to high power mode) was essentially negligible as far as PWM was concerned even with a ceramic resonator instead of a crystal, so the errors are only in the buffer switching IC voltage drops and rise/fall edge characteristics. I think I just used a 74HC family IC as the buffer.Richard