Need a 500VDC Calibration Voltage - Page 1
Forum section: electronics / projects

author: med6753
author_rank: Super Contributor
timestamp: November 08, 2015, 06:20:19 pm
content: Background: Tek 2465 DMS with DMM option. Attempting to get the DCV function fully calibrated. 2 of the calibration constants required are 190.0V and 500.0V. I used this inverter to calibrate the 190.0V constant and was successful...http://www.amazon.com/gp/product/B010UGJF1I?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00Let me state right off that I've been unable to find a schematic for this device. Somehow I would like to get the 500.0V calibrated and here's my thought process. Purchase a 2nd inverter and set both of them to 250V each and connect the outputs in series just like I had an AC transformer and I connected the secondaries in series to achieve a higher voltage. But here's the rub. I did verify that -V in and -V out are on a common bus. So I THINK I'm risking magic smoke if I attempt this. Perhaps even blow out the input supply. My other thought process to isolate everything is to put each inverter on separate battery inputs. Would that work? I can't seem to wrap my head around this and looking for help.I'm well aware of the safety aspects here and quite frankly I don't like working with high voltages. This circuit would only be built up long enough to get the calibration done and then dismantled.Thanks.

author: SeanB
author_rank: Super Contributor
timestamp: November 08, 2015, 06:25:18 pm
content: 2 12V SLA batteries should provide enough power to drive the inverters till you have finished the calibration. Just have each battery sitting on it's own insulatingf plastic sheet and have them fully charged and disconnected from the charger before starting. Floating supply means no smoke.

author: Zero999
author_rank: Super Contributor
timestamp: November 08, 2015, 07:07:52 pm
content: How accurate do you think that inverter is? It may not be up to the task.What sort of accuracy do you require?You could build your own reference by connecting the mains to a step-up transformer or capacitive multiplier and amplifying a voltage reference IC.

author: dom0
author_rank: Super Contributor
timestamp: November 08, 2015, 07:45:34 pm
content: If you have a insulation transformer you could use a delon circuit to get about ~650 Vpk from 230 V. Those 650 V can then be regulated by a (ground referenced) op-amp and two high-voltage transistors to an external reference.

author: Paul Price
author_rank: Super Contributor
timestamp: November 08, 2015, 08:54:59 pm
content: Are you willing to breadboard/build a simple circuit or require that the calibrator 500V sourced be off-the-shelf?Do you have another accurate DVM that can exact that a self-built device is outputting 500V at the accuracy you require?

author: med6753
author_rank: Super Contributor
timestamp: November 08, 2015, 10:56:35 pm
content: Quote from: Hero999 on November 08, 2015, 07:07:52 pmI used 1 inverter to calibrate the 190V constant. I used a Fluke 87 to set it to 190.0V and it remained stable. The processor in the 2465 accepted it and calibrated. If it had not been accurate I would have gotten an "Out of Limits" message. Hence I think 2 of them would be accurate enough.

author: med6753
author_rank: Super Contributor
timestamp: November 08, 2015, 10:59:46 pm
content: Quote from: Paul Price on November 08, 2015, 08:54:59 pmI'd rather breadboard something. I have a Fluke 87 to set it accurately. This method was successful in calibrating the 190V. If it wasn't accurate enough I would have gotten an "Out of limits" message from the 2465 DMM.

author: med6753
author_rank: Super Contributor
timestamp: November 08, 2015, 11:02:08 pm
content: Quote from: dom0 on November 08, 2015, 07:45:34 pmI do have an isolation transformer but I'm in the USA and it's 120VAC. And I live in an apartment and no access to 230VAC.

author: med6753
author_rank: Super Contributor
timestamp: November 08, 2015, 11:07:52 pm
content: Quote from: SeanB on November 08, 2015, 06:25:18 pmThanks for your input. Nice to see that my thought process is on the right track.

author: Seekonk
author_rank: Super Contributor
timestamp: November 08, 2015, 11:20:29 pm
content: I like electronic wall warts and this might be an interesting use. Tap a diode off the FET high side as a boost converter into a capacitor, likely two or three in series to get enough voltage. Monitor that voltage with a LM431 that drives the opto and connect the input and output commons. That would give you a good use for the isolation transformer you have. Many of those little chips have a 700V rating. A little on the edge but it will likely work. Of course this is an entire project in itself.

author: dom0
author_rank: Super Contributor
timestamp: November 09, 2015, 01:34:17 am
content: Quote from: med6753 on November 08, 2015, 11:02:08 pmYou can cascade voltage doublers

author: Paul Price
author_rank: Super Contributor
timestamp: November 09, 2015, 02:29:54 am
content: The Fluke87 is your reference standard and is the qualifier for your calibration voltages, not the 2465 DMS. How can the 2465 tell you that your calibrating voltage is "out of limits" when it is itself yet uncalibrated? It can only show an over range input voltage condition exits.Do you have any of these: a 555 timer chip and a breadboard and resistors and HV capacitors, assorted small value low-Voltage capacitors, a HV switching NPN switching transistor or a HV N-MOSFET, a toroidal core, a SMPS P/S HF transformer, an HV fast switching diode that can handle 800V or even some 1N4006 rectifier diodes or a SMPS module you could get from of a discarded DVD/VCR or even a DC wallwart/brick for a laptop that gives you an output in the 18-22V range?

author: med6753
author_rank: Super Contributor
timestamp: November 09, 2015, 03:45:20 am
content: Quote from: Paul Price on November 09, 2015, 02:29:54 amHere's a link to the manual. Pages 4-7 and 4-8...http://www.ko4bb.com/manuals/129.33.205.136/Tek_2465_DMM_Option_Service_Nov85.pdfThe calibration constants for the DCV are .19V, 1.9V, 19V, 190V, and 500V. I used an LM723 to set a precise 19.0V then used a voltage divider to get .19V and 1.9V. I used the inverter to get 190.0V. The Fluke 87 initially set the voltages. I then applied those set points as per the manual. I verified afterwards that the 2465 DMM tracked properly to the standards I have. Prior to the calibration it was way off. I'm not sure how it figured out that the voltages applied were within limits but it seemed to work. I'm not arguing with success.QuoteI have some of the parts. I've just recently gotten back into the hobby after about 15 years inactivity. Do you have a schematic?

author: Zero999
author_rank: Super Contributor
timestamp: November 09, 2015, 08:00:24 am
content: An amplifier can be added to a voltage reference to produce an accurate high voltage output. The schematic below gives 250VDC but it could easily be modified for 500V.