Author Topic: Project KX : DIY calibrator / reference source/meter  (Read 176867 times)

0 Members and 1 Guest are viewing this topic.

Offline TiNTopic starter

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Project KX : DIY calibrator / reference source/meter
« Reply #200 on: May 06, 2015, 04:18:07 am »
If you just looking for reference I would suggest to get LM399A , as it provides still awesome performance and stability. And it does not need unobtanium resistors, just usual precision for few USD to keep zener current stable. If 7V direct is enough for your needs, then you can get everything for less than 30$.

Making stable 10V will take more money, as still need good resistors for that, as output drift will come mainly from their tempco.
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Offline Theboel

  • Frequent Contributor
  • **
  • Posts: 278
  • Country: id
Re: Project KX : DIY calibrator / reference source/meter
« Reply #201 on: May 06, 2015, 06:55:32 am »
Thank You For Your input Yes I do not need (yet) something better than my 34410 can measure, for tempco I far from expert but my idea are put the reference board in very heavy steel iron pipe and use maybe 6 psi 99,9 % nitrogen to avoid humidity and then wrap it with some insulator for temperature control let say do it 2 times with 2 separated oven system like Double OCXO system.
maybe its working maybe not let find out soon (any input is very welcome)
but to made its works I need to conection between the ref board to outside, what is conector You suggest is "good enough" for supply voltage and measurement point ?
« Last Edit: May 06, 2015, 09:32:33 am by Theboel »
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 3221
  • Country: de
Re: Project KX : DIY calibrator / reference source/meter
« Reply #202 on: May 06, 2015, 07:00:22 am »
This project is far away from my budget but may be I can handle a "cheaper" version of the reference unit.
any sugestion for Visahy resistor replacement ?

If its only the 5 resistors of the LTZ1000(A) itself you can use also precision wire wound resistors with a T.C. below 3 ppm/K.
As their T.C. affects only with a dampening of the cirquit to the output.
You can use e.g. the resistors of Edwin for this purpose.
https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg602719/#msg602719

For a 7V to 10V transfer you will have to use a very good matched set of resistors (at extra costs).

with best regards

Andreas

 

Offline TiNTopic starter

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Project KX : DIY calibrator / reference source/meter
« Reply #203 on: May 12, 2015, 12:21:37 pm »
I bet no one complain about this lot I just received from 'bay today...



It's about 4kg of resistor networks.

Most of it are usual 100-200ppm/K ones, in alumina and plastic DIP/SIP packages, but few items are standing out:







RIFA PBA 3002/7 with pair of 732 ohm resistors, and RIFA PBA 3002/5 with pair of 1200 ohm resistors.
Welvyn ceramic module with some 100Kyish resistors and low-ohm resistor on back (heater?). It have also two rusty thingy's on top (diodes?)
Some ceramic module (SIP from NORTEL, marked on back QMS9A with pair of quad opamps and some passives around
ERESISTOR ceramic module with some resistors on them
Maxitech TF1019 module with pair of 10 ohm resistors.

If anyone have data about these - please share :)
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Offline TiNTopic starter

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Project KX : DIY calibrator / reference source/meter
« Reply #204 on: May 12, 2015, 12:26:55 pm »
And back to topic - here some nice HV gear I got for output stages. UltraVolt 4W DC-DC modules, two with adjustable +1000VDC, and one +6000VDC :)





These bad boys are nice for their size, given performance specs:
* 4W output, 12V input
* Ripple on output <0.0005%
* Output voltage monitor via integrated divider
* uMetal-shielding
* >400,000 Hrs MTBF @ 65°C
* 55.6mA/V output current monitor
* Output voltage regulation <0.01% no load to full load
« Last Edit: May 12, 2015, 12:28:30 pm by TiN »
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Offline TiNTopic starter

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Project KX : DIY calibrator / reference source/meter
« Reply #205 on: May 12, 2015, 12:31:58 pm »
Thanks all for feedback on DAC schematics, I will work on it this week and release REV2 for discussion at weekend.  :)
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Offline splin

  • Frequent Contributor
  • **
  • Posts: 999
  • Country: gb
Re: Project KX : DIY calibrator / reference source/meter
« Reply #206 on: May 12, 2015, 02:43:14 pm »
Did you manage to find any decent quality low thermal EMF banana sockets/binding posts at a reasonable price?
 

Offline TiNTopic starter

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Project KX : DIY calibrator / reference source/meter
« Reply #207 on: July 07, 2015, 05:35:31 pm »
No, had no much luck. I think I'll go triax for sensitive stuff anyway as 2nd choice.

Tested HV DC-DC module, working like a charm. Love adjustment option, would be easy too use as coarse adjustment output voltage.

Here are some testlog photos for your enjoyment..

Forgive crude setup, don't any good HV caps at moment to decouple output. Just proof of concept test.

Keithley 2400 (in center top): +12V power to UltraVolt 1A12-P4-F-M DC-DC module
Left Keithley 2001: Output voltage measure
Right Keithley 2001: Remote Adjust Input measure. This voltage sourced from EDC MV106 DC Standard
Keithley 2002 (in center bottom): +5VDC Reference Output from UltraVolt



Here are check points at 100V, 200V and 1000VDC





Also checked with Fluke 87V. Little meter spot-on agree to K2001, and measures only up to 1090.4VDC, after that just gives OL.
I don't have anything ready for 6KV DC-DC module, so will test that one later.



Wish I'd have negative supply as well. Eh, one thing at a time, will come to that later.
Now time to go back to low-voltage stuff on control side..
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Offline TiNTopic starter

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Project KX : DIY calibrator / reference source/meter
« Reply #208 on: August 03, 2015, 10:50:19 am »
ADC works in progress, test module design of integrating long-scale topology, to fit Keithley 2001/2002 DMMs for debug/evaluation.



Same formfactor as native ADC.

* Digital : ALTERA 5M1270T144 CPLD
* Power : LDO Linear LT3065EDD 1.8V and 3.3V
* Level translation : SN74LVCC4245APW
* Clock : FOX924B-12.000 TCXO
* PCB: 4-layer FR4

Analog section going to be revamped K2002's, with modern parts.
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Offline TiNTopic starter

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Project KX : DIY calibrator / reference source/meter
« Reply #209 on: August 04, 2015, 04:25:48 am »
Alright dear nuts, here's what is in 2002 as voltage reference input buffer/ratio block






This piece of schematic is taking single +7.2V from LTZ1000A and converting it into +12.080V, +2.4000V, -2.4000V, -7.200V and -12.000V.
5K and 20K resistors are BI Nichrome Resistor Networks, 0.05% ratio tolerance, 25ppm/K TCR and 5ppm tracking.

I'm thinking of LT5400's with 1K/10K values, but that would be rather expensive :(.
Also idea to change OP27 to LTC2057, to get lower noise below 10Hz band, but not sure how that would help yet.

For playing with this piece in you can download LTSpiceIV schematic
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Online Kleinstein

  • Super Contributor
  • ***
  • Posts: 14072
  • Country: de
Re: Project KX : DIY calibrator / reference source/meter
« Reply #210 on: August 04, 2015, 08:48:58 am »
The low frquency noise of the LTZ1000 is way higher than that of OPs like OP27. So there is no real need to replace the OPs because of the LF noise. Long term drift may be a reson for a replacement. The higer frequency noise of the LTC2057 is considerably worse.

So it really depends on what the voltages are used for.
 

Offline TiNTopic starter

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Project KX : DIY calibrator / reference source/meter
« Reply #211 on: August 04, 2015, 10:12:34 am »
The output for voltages is multi-slope long-scale discrete ADC.
Primary reference source would be multiple LTZ1000 with some filtering, not direct output, so hopefully noise would be possible to reduce.



Little placement update. Going with 25ppm/5ppm tracking Vishay 8R networks instead of LT5400.
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Offline plesa

  • Frequent Contributor
  • **
  • Posts: 965
  • Country: se
Re: Project KX : DIY calibrator / reference source/meter
« Reply #212 on: August 04, 2015, 10:35:34 am »
I tried to check the parameters and pricing for BI NiCr resistors and they looks like obsolete. If we needs cheaper alternative  you can use NOMC from Vishay with same spec and price about 10 USD/pc which is half of LT5400. But NOMC are not offered in divider configuration.Another alternative can be Vishay RMKMS, but their price is almost same as LT5400.
The best will be prepare PCB layout for two alternatives.
« Last Edit: August 04, 2015, 10:43:58 am by plesa »
 

Offline TiNTopic starter

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Project KX : DIY calibrator / reference source/meter
« Reply #213 on: August 04, 2015, 11:10:53 am »
That's what I used for now, they are okay in price at digikey, and going in 8-piece arrays. I don't need divider configuration either so far.
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Offline plesa

  • Frequent Contributor
  • **
  • Posts: 965
  • Country: se
Re: Project KX : DIY calibrator / reference source/meter
« Reply #214 on: August 04, 2015, 11:30:56 am »
Let me know if you needs some testing of them. I have buch of LT5400 and NOMC in drawer from different experiment 752 Junior :)
Based on my experiments LT5400 provides much better matching for affordable price (compared 10k versions )
« Last Edit: August 04, 2015, 12:04:02 pm by plesa »
 

Offline Kalvin

  • Super Contributor
  • ***
  • Posts: 2145
  • Country: fi
  • Embedded SW/HW.
Re: Project KX : DIY calibrator / reference source/meter
« Reply #215 on: August 04, 2015, 01:01:05 pm »
One question about the precision resistors: Can one use less precise resistors and perform some kind of software-based calibration. The less precision "Metal Film Resistors - Through Hole 1/8watt 10Kohms .1% 5ppm" cost less than $1 each. Sorry if this has been asked already before.
 

Offline plesa

  • Frequent Contributor
  • **
  • Posts: 965
  • Country: se
Re: Project KX : DIY calibrator / reference source/meter
« Reply #216 on: August 04, 2015, 01:29:27 pm »
Main reason is matching ( temperature and ratio), If you use the THT resistors you will needs extra time to find match and you will needs to purchase bigger batch of resistors, which will be at the end more expensive. E.g the cheapest NOMC is about 2.5 USD and LT5400 in A grade is 16 USD.
« Last Edit: August 04, 2015, 01:42:49 pm by plesa »
 

Offline TiNTopic starter

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Project KX : DIY calibrator / reference source/meter
« Reply #217 on: August 04, 2015, 01:45:42 pm »
Like plesa said, it's stability and ratio matching what is important in application like this, not accuracy. On LT5400 it's awesome 7.5%, making it worse than usual thinfilm of 1c. What's is important there, that all four(or more) resistors in networks are embedded on single mica or ceramic substrate, with same kind of material and process, so even if they all drift, they will drift very closely together. So absolute ratio would stay particularly constant, or at least close to that.

That's why it does not really matter if it's 0.001% or 0.1% or 7.5% absolute accuracy tolerance there. Other thing is that more stable resistors are also usually more accurate, is a "side-effect" of how things manufactured. Sometimes you need absolute accuracy (for example for precision KVD or voltage divider, where value of resistors are important), sometimes you need just stability (then stuff like LT5400 will work good), sometimes you need both (then you need go custom networks, like Vishay foil networks, and prepare to pay gold for it).

Also worth a note, that it's not always tempco that important, but other things like power coefficient (resistor will drift with current flowing thru it, as resistive element will heatup itself), sensitivity to environment humidity and mechanicals, etc.
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Offline plesa

  • Frequent Contributor
  • **
  • Posts: 965
  • Country: se
Re: Project KX : DIY calibrator / reference source/meter
« Reply #218 on: August 04, 2015, 02:02:12 pm »
Sometimes you need absolute accuracy (for example for precision KVD or voltage divider, where value of resistors are important).

For KVD you not needs absolute accuracy, but the ratio. Currently I do not see on market matched network which contains 11 matched resistors for homemade KVD ( only 8).
Nice trick is made by Mr. Hamon described by Mr. Hoffmann http://conradhoffman.com/HamonResistor.html or by Joe Geller http://www.gellerlabs.com/752AJunior.htm
I'm little bit worried about the long term stability and overheating during soldering.
 

Offline Kalvin

  • Super Contributor
  • ***
  • Posts: 2145
  • Country: fi
  • Embedded SW/HW.
Re: Project KX : DIY calibrator / reference source/meter
« Reply #219 on: August 04, 2015, 02:03:43 pm »
What's is important there, that all four(or more) resistors in networks are embedded on single mica or ceramic substrate, with same kind of material and process, so even if they all drift, they will drift very closely together. So absolute ratio would stay particularly constant, or at least close to that. 
This is something that cannot be calibrated away with the software.

Thank you guys for you excellent explanation.
 

Offline plesa

  • Frequent Contributor
  • **
  • Posts: 965
  • Country: se
Re: Project KX : DIY calibrator / reference source/meter
« Reply #220 on: August 04, 2015, 02:07:53 pm »
What's is important there, that all four(or more) resistors in networks are embedded on single mica or ceramic substrate, with same kind of material and process, so even if they all drift, they will drift very closely together. So absolute ratio would stay particularly constant, or at least close to that. 
This is something that cannot be calibrated away with the software.

Thank you guys for you excellent explanation.

If you have for example 4 matched resistors thy can have different resistance vs temperature slope (tempco) or can be oposite (tempco is defined +/-). This cannot be calibrated easily unless you add the temperature sensor close to them.
« Last Edit: August 04, 2015, 02:17:42 pm by plesa »
 

Offline Kalvin

  • Super Contributor
  • ***
  • Posts: 2145
  • Country: fi
  • Embedded SW/HW.
Re: Project KX : DIY calibrator / reference source/meter
« Reply #221 on: August 04, 2015, 02:45:29 pm »
What's is important there, that all four(or more) resistors in networks are embedded on single mica or ceramic substrate, with same kind of material and process, so even if they all drift, they will drift very closely together. So absolute ratio would stay particularly constant, or at least close to that. 
This is something that cannot be calibrated away with the software.

Thank you guys for you excellent explanation.

If you have for example 4 matched resistors thy can have different resistance vs temperature slope (tempco) or can be oposite (tempco is defined +/-). This cannot be calibrated easily unless you add the temperature sensor close to them.
True. I will write this here how I understand this:

So, if the resistors are on the same substrate and package, their temperatures and their tempcos will be essentially identical so their resistance ratio will be unaffected by temperature, or at least their ratio will change as little as possible. And if any current flow through one resistor changes the temperature that resistor, the heat will be spread to the other resistors keeping the resistance ratio unaffected.

If the resistors are discrete resistors, although how precise and similar tempcos, they would propably have different temperatures as any current flow may cause heating or any other component nearby can create a heat gradient, thus the ratio will not be accurate any more.

In high precision measurements this should take into account and the resistors should be on the same substrate and package if the resistor ratio is important.
 

Offline plesa

  • Frequent Contributor
  • **
  • Posts: 965
  • Country: se
Re: Project KX : DIY calibrator / reference source/meter
« Reply #222 on: August 04, 2015, 02:52:31 pm »
Yes, you understand it correctly. For example in some KV dividers the first stage is in oil bath to keep all resistors on same temperature.
 

Offline TiNTopic starter

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Project KX : DIY calibrator / reference source/meter
« Reply #223 on: August 04, 2015, 04:12:36 pm »
No problem, going with them anyway, seems best cost/performance solution so far, and available too.
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Offline ManateeMafia

  • Frequent Contributor
  • **
  • Posts: 730
  • Country: us
Re: Project KX : DIY calibrator / reference source/meter
« Reply #224 on: August 04, 2015, 05:01:12 pm »
Nice find on the NOMCA. I was looking at using the ORN based resistors for an ovenized application. Comparing the two I can see the NOMCA would be a better choice for moisture protection.

I am guessing that connecting every other resistor would improve temperature tracking or am I missing something obvious?
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf