Voltage current calibrator 0 to +/- 10V, and 0 to 40mA 0.001%
Generate any accurate voltage 0 to +/-10V with 20uV step and 0 to 40mA 100nA for your design or for multimeter, oscilloscope calibration source
I bought a broken oscilloscope from EBay and in order to take full advantage of its features, it had to be calibrated in voltage and, in current. Normally requested calibration values are 1.000V or 10.000mA… but for this oscilloscope, specific voltage and current sources were needed: +/- 1.7694V and 20.253mA.
There are many calibrator solutions on the market but these devices are out of my budget or, did not have the required resolution.
So, the solution for me was to build a calibrator by myself.
Video link : https://youtu.be/i8ZxOXWNTnU
Specifications
Output voltage 0 to +/- 10V with 20uV resolution.
Current 0 to 40mA, resolution 100nA.
Accuracy 10ppm (10 parts per million) at 21°C which is 0.001% at 21°C.
Easy to calibrate by soft.
Power supply via USB. Battery option.
3.5”Color touch screen to avoid front panel buttons machining.
1 Schematic
There are 5 main blocks in my design: The power supply The voltage reference The DAC around the AD5791 The current generator The HMI, with its microcontroller
The power supply:
Power is supplied from an USB PSU providing at least 500mA. The 5V supplied is divided into two separate parts. One way feeds the HMI with the microcontroller. The other way feeds the DAC and voltage reference in +/- 15V, using an isolated up converter. The +/- 15V output is filtered and goes into two linear regulators, both regulators are low drop out voltage and low noise.
The voltage reference:
This is the most critical element in this circuit. If we need a reference voltage of 10.00000V at +/- 10uV, we want this forever but in the real world, it can’t be reach. The topic of voltage references is a science in itself, on the web there are dozens of articles and specialists who discuss this subject in order to push the limits of features such as: noise, stability in ppm / ° C in the short and long term, hysteresis, thermoelectric EMF, piezoelectric… In your favorite search engine let see the Rolls of voltage references: the LTZ1000 with a drift of 0.05ppm / ° C. Some authors have produced voltage references with amazing and beautiful PCBs with very low temperature coefficient resistor in oil filled metal housing. After testing three voltage references (LTC6655, ADR445, MAX6350ESA), I chose the MAX6350ESA from Maxim which I found to be more stable over time with 5V output. With both Op Amp U10A / B inside the AD8676 (Dual low noise, low offset drift voltage Op amp) +10.48V and - 10.48V are produced. The resistors R16, R17, R18, R19, R20 around the AD8676 are low temperature drift resistors (better than 2ppm / ° C).
The DAC around the AD5791
The chosen DAC is AD5791 for its 20-bit and for its linearity of 1ppm. This linearity feature simplifies the calibration: Only the 0V point and 10V point need to be adjusted. The 20-bit DAC1220 with 15ppm of linearity requires a correction table so I didn’t choose it. The schematic around the AD5791 uses the elements of the Analog device Eval board. The DAC receives the reference voltages of +10.48V and - 10.48V which produces a step of roughly 20uV. The output voltage Vout = ((+ Vref - (- Vref)) / 2e20 -1) x code –Vref Or, approximately Vout = 2 x code -10.48576 The calibrator output is software limited to +/- 10V. This gives a large capability to compensate the offset error at 0V
The precision current source
The four main components of the precision current source are U7 AD8276 instrument amplifier, Q1 PZT1222, U8 8677 and R10 100ohm. Q1 provides the current to the load. This current flows through the R10 (measurement resistor) and the relay and then, goes to the load under test to finally return to ground. The voltage on R10 terminal is measured by U8 and U7 is compared to the reference voltage supplied by the DAC AD5791. Output source current = VDAC / R10 or VDAC / 100 The current is limited to 40mA by the software to avoid voltage measurement drift in R10 due to thermal heating inside R10 and Q1. The temperature coefficient of resistance R10 is critical and must be as low as 0.2ppm / ° C. For this reason, the implantation of Q1 is as far as possible from R10 and of course from reference voltages.
The HMI with its microcontroller
This part is done by an ulcd35DT module from 4D system which integrates a 3.5 "resistive color touch screen and the microcontroller. The IDE is free and contains the touch button function libraries for this project. The code is a simplified form of C.
The GUI is made as follows:
Touch buttons and digits are images stored on the micro SD card. Each image has x,y coordinates on the touchscreen. When the screen is touched, an interrupt is generated to give which image has been touched and the dedicated action occurs.
Operation: the screen consists of a touch-sensitive encoder wheel and three buttons. The +/- buttons of the encoder wheels select the output value. The "sign" buttons reverse the sign of the output voltage. Inactive in current mode.The "000" button sets the output to 0V The "Volt / mA" button selects the current or voltage mode
2 Calibration
The calibrator needs to be aged before its calibration.
Voltage reference aging
As any reference voltage source, it has to be aged to improve long term stability. I chose 1000 hours at room temperature. After 41 days (1000 hours) over 1 week, the reference is stable at 4.99994V and the two references 10.50050 and -10.49867 are stable at +/- 10uV.
Calibration of the…calibrator
A minimum 6.5 digit multimeter is required. I used my Agilent 34410APressing and holding the "Sign" button for 8 seconds clear all calibration factors
Calibration in voltage mode:
Long press for 5 seconds on the "000" button to start the calibration. Press the “Volt/mA” button to interrupt the calibration sequence. Use the “+” and “-“buttons of the encoder wheels to obtain 0V +/- 15uV on the multimeter. Wait about 10 seconds to stabilize. Press "000": "cal stored" is displayed for 2 seconds then the encoder wheels display 10.00000. Using the encoder wheels, select the value necessary to generate 10.00000V +/- 15uV.
Calibration in current mode:
Long press for 5 seconds of the "000" button to start the calibration.
The encoder wheels display 00.0100mA. Using the “+”and ”-“ buttons on the encoder wheels, select the value necessary to generate 10uA +/- 100nA on the multimeter.
Press "000" : "cal stored" is displayed for 2 seconds then the encoder wheels display 30.0000. Using the encoder wheels, select the value necessary to generate 30mA +/- 100nA.
3 Other
Enclosure
The calibrator PCB with its display is designed to fit the Hammond Enclosure
Battery option
The calibrator PCB is designed to install a Chinese battery charger and discharger (ref DDO4CVSA) from Eletechsup manufacturer but it has not been used here finally because it heated too much.
Future improvement
Any temperature variation modifies the calibrator output accuracy. I put a thermal sensor (NTC) on the PCB at the back of the voltage reference. May be I will use this thermal sensor for correcting the drift of the reference voltage or may be I will ovenize the reference voltage area on PCB....
4 References
Long term characterization of voltage references from Hubert Halloin, Pierre Prat, and Julien Brossard https://arxiv.org/pdf/1312.5101.pdf
Current Sources & Voltage References from Linden T. Harrison
https://doc.xdevs.com/doc/_Metrology/Print%20Ver.%20-%20Current_Sources_and_V%20_Refs.pdf
https://xdevs.com/article/kx-ref/ for LTZ1000
AD5791 Eval board
https://www.analog.com/en/design-center/evaluation-hardware-and-software/evaluation-boards-kits/eval-ad5791.html
5 Improvements June 19th 2021
Version 1-3
Main Improvements
Voltage Drift
The drift can be due (not only) to the temperature variation and to the age of the component.
1) Aging More a reference source is old, more it is stable. To speed up the aging I did three up and down temperature cycles from -20°C to 20°C. After more than 1000 hours of power ON, I measured the output during 24 hours and the stability has become roughly around 2 ppm. See test results sheet. 2) Temperature coefficient The drift of the output voltage versus temperature (TEMPCO) is measured in ppm/volt. So, with a 10V output signal, 1 ppm gives 10 uV.
My lab temperature can be from 15°C to 25°C, not in one day of course, but, if the output has a TEMPCO of 2.5ppm/°C, the voltage output can change up to 250 uV in this temperature range.
I used a DIY thermal chamber with a temperature controller. I did a 5 hours temperature cycle from 15°C to 40°C. I got 1 ppm/°C. So, for 10 V output I got 9.999823 V at 42°C and 10.000062 V at 14°C. This gives 1 ppm/°C. See “with vs_without heater” excel files.
I wondered if I could do a better TEMPCO if I ovenized the reference. The goal was to heat the reference circuit to stabilize the temperature. I chose a set point at 55°C. So, I built a temperature controlled heater on little PCB and I glued it on the bottom side of the reference circuit of the calibrator. I put the calibrator in my thermal chamber, I did a 5 hours temperature cycle from 15°C to 40°C and I got a drift of the output voltage of 26 uV so this gives a TEMPCO less than 0.2ppm/°C. Five time better without heater!
New PCB
Correction of layout error, improvement of the output sense layout against external load.
Now internal is resistance: 0.016 Ohm. The maximum load is 5 mA to save accuracy.
Modification of reference circuit position to place a case surrounding the reference. I used my 3D printer to print the case.
Diagram
Correction of label errors. Added measure of reference temperature for alarm and warm up for the software and display. Output sense modifications.
Software
Added messages during calibration process
Added warm up and heater alarm messages
Added message “open loop” in mode current
Bug correction on tactile functionalities
6 Measurement and plots update July 08th,2021
Add noise plots measurement with PN9000 noise analyser instrument
- Calibrator_noise+10V.jpg- Calibrator_noise-10V.jpg
There are many calibrator solutions on the market but these devices are out of my budget or, did not have the required resolution.
So, the solution for me was to build a calibrator by myself.
Video link : https://youtu.be/i8ZxOXWNTnU
Specifications
Output voltage 0 to +/- 10V with 20uV resolution.
Current 0 to 40mA, resolution 100nA.
Accuracy 10ppm (10 parts per million) at 21°C which is 0.001% at 21°C.
Easy to calibrate by soft.
Power supply via USB. Battery option.
3.5”Color touch screen to avoid front panel buttons machining.
1 Schematic
There are 5 main blocks in my design: The power supply The voltage reference The DAC around the AD5791 The current generator The HMI, with its microcontroller
The power supply:
Power is supplied from an USB PSU providing at least 500mA. The 5V supplied is divided into two separate parts. One way feeds the HMI with the microcontroller. The other way feeds the DAC and voltage reference in +/- 15V, using an isolated up converter. The +/- 15V output is filtered and goes into two linear regulators, both regulators are low drop out voltage and low noise.
The voltage reference:
This is the most critical element in this circuit. If we need a reference voltage of 10.00000V at +/- 10uV, we want this forever but in the real world, it can’t be reach. The topic of voltage references is a science in itself, on the web there are dozens of articles and specialists who discuss this subject in order to push the limits of features such as: noise, stability in ppm / ° C in the short and long term, hysteresis, thermoelectric EMF, piezoelectric… In your favorite search engine let see the Rolls of voltage references: the LTZ1000 with a drift of 0.05ppm / ° C. Some authors have produced voltage references with amazing and beautiful PCBs with very low temperature coefficient resistor in oil filled metal housing. After testing three voltage references (LTC6655, ADR445, MAX6350ESA), I chose the MAX6350ESA from Maxim which I found to be more stable over time with 5V output. With both Op Amp U10A / B inside the AD8676 (Dual low noise, low offset drift voltage Op amp) +10.48V and - 10.48V are produced. The resistors R16, R17, R18, R19, R20 around the AD8676 are low temperature drift resistors (better than 2ppm / ° C).
The DAC around the AD5791
The chosen DAC is AD5791 for its 20-bit and for its linearity of 1ppm. This linearity feature simplifies the calibration: Only the 0V point and 10V point need to be adjusted. The 20-bit DAC1220 with 15ppm of linearity requires a correction table so I didn’t choose it. The schematic around the AD5791 uses the elements of the Analog device Eval board. The DAC receives the reference voltages of +10.48V and - 10.48V which produces a step of roughly 20uV. The output voltage Vout = ((+ Vref - (- Vref)) / 2e20 -1) x code –Vref Or, approximately Vout = 2 x code -10.48576 The calibrator output is software limited to +/- 10V. This gives a large capability to compensate the offset error at 0V
The precision current source
The four main components of the precision current source are U7 AD8276 instrument amplifier, Q1 PZT1222, U8 8677 and R10 100ohm. Q1 provides the current to the load. This current flows through the R10 (measurement resistor) and the relay and then, goes to the load under test to finally return to ground. The voltage on R10 terminal is measured by U8 and U7 is compared to the reference voltage supplied by the DAC AD5791. Output source current = VDAC / R10 or VDAC / 100 The current is limited to 40mA by the software to avoid voltage measurement drift in R10 due to thermal heating inside R10 and Q1. The temperature coefficient of resistance R10 is critical and must be as low as 0.2ppm / ° C. For this reason, the implantation of Q1 is as far as possible from R10 and of course from reference voltages.
The HMI with its microcontroller
This part is done by an ulcd35DT module from 4D system which integrates a 3.5 "resistive color touch screen and the microcontroller. The IDE is free and contains the touch button function libraries for this project. The code is a simplified form of C.
The GUI is made as follows:
Touch buttons and digits are images stored on the micro SD card. Each image has x,y coordinates on the touchscreen. When the screen is touched, an interrupt is generated to give which image has been touched and the dedicated action occurs.
Operation: the screen consists of a touch-sensitive encoder wheel and three buttons. The +/- buttons of the encoder wheels select the output value. The "sign" buttons reverse the sign of the output voltage. Inactive in current mode.The "000" button sets the output to 0V The "Volt / mA" button selects the current or voltage mode
2 Calibration
The calibrator needs to be aged before its calibration.
Voltage reference aging
As any reference voltage source, it has to be aged to improve long term stability. I chose 1000 hours at room temperature. After 41 days (1000 hours) over 1 week, the reference is stable at 4.99994V and the two references 10.50050 and -10.49867 are stable at +/- 10uV.
Calibration of the…calibrator
A minimum 6.5 digit multimeter is required. I used my Agilent 34410APressing and holding the "Sign" button for 8 seconds clear all calibration factors
Calibration in voltage mode:
Long press for 5 seconds on the "000" button to start the calibration. Press the “Volt/mA” button to interrupt the calibration sequence. Use the “+” and “-“buttons of the encoder wheels to obtain 0V +/- 15uV on the multimeter. Wait about 10 seconds to stabilize. Press "000": "cal stored" is displayed for 2 seconds then the encoder wheels display 10.00000. Using the encoder wheels, select the value necessary to generate 10.00000V +/- 15uV.
Calibration in current mode:
Long press for 5 seconds of the "000" button to start the calibration.
The encoder wheels display 00.0100mA. Using the “+”and ”-“ buttons on the encoder wheels, select the value necessary to generate 10uA +/- 100nA on the multimeter.
Press "000" : "cal stored" is displayed for 2 seconds then the encoder wheels display 30.0000. Using the encoder wheels, select the value necessary to generate 30mA +/- 100nA.
3 Other
Enclosure
The calibrator PCB with its display is designed to fit the Hammond Enclosure
Battery option
The calibrator PCB is designed to install a Chinese battery charger and discharger (ref DDO4CVSA) from Eletechsup manufacturer but it has not been used here finally because it heated too much.
Future improvement
Any temperature variation modifies the calibrator output accuracy. I put a thermal sensor (NTC) on the PCB at the back of the voltage reference. May be I will use this thermal sensor for correcting the drift of the reference voltage or may be I will ovenize the reference voltage area on PCB....
4 References
Long term characterization of voltage references from Hubert Halloin, Pierre Prat, and Julien Brossard https://arxiv.org/pdf/1312.5101.pdf
Current Sources & Voltage References from Linden T. Harrison
https://doc.xdevs.com/doc/_Metrology/Print%20Ver.%20-%20Current_Sources_and_V%20_Refs.pdf
https://xdevs.com/article/kx-ref/ for LTZ1000
AD5791 Eval board
https://www.analog.com/en/design-center/evaluation-hardware-and-software/evaluation-boards-kits/eval-ad5791.html
5 Improvements June 19th 2021
Version 1-3
Main Improvements
Voltage Drift
The drift can be due (not only) to the temperature variation and to the age of the component.
1) Aging More a reference source is old, more it is stable. To speed up the aging I did three up and down temperature cycles from -20°C to 20°C. After more than 1000 hours of power ON, I measured the output during 24 hours and the stability has become roughly around 2 ppm. See test results sheet. 2) Temperature coefficient The drift of the output voltage versus temperature (TEMPCO) is measured in ppm/volt. So, with a 10V output signal, 1 ppm gives 10 uV.
My lab temperature can be from 15°C to 25°C, not in one day of course, but, if the output has a TEMPCO of 2.5ppm/°C, the voltage output can change up to 250 uV in this temperature range.
I used a DIY thermal chamber with a temperature controller. I did a 5 hours temperature cycle from 15°C to 40°C. I got 1 ppm/°C. So, for 10 V output I got 9.999823 V at 42°C and 10.000062 V at 14°C. This gives 1 ppm/°C. See “with vs_without heater” excel files.
I wondered if I could do a better TEMPCO if I ovenized the reference. The goal was to heat the reference circuit to stabilize the temperature. I chose a set point at 55°C. So, I built a temperature controlled heater on little PCB and I glued it on the bottom side of the reference circuit of the calibrator. I put the calibrator in my thermal chamber, I did a 5 hours temperature cycle from 15°C to 40°C and I got a drift of the output voltage of 26 uV so this gives a TEMPCO less than 0.2ppm/°C. Five time better without heater!
New PCB
Correction of layout error, improvement of the output sense layout against external load.
Now internal is resistance: 0.016 Ohm. The maximum load is 5 mA to save accuracy.
Modification of reference circuit position to place a case surrounding the reference. I used my 3D printer to print the case.
Diagram
Correction of label errors. Added measure of reference temperature for alarm and warm up for the software and display. Output sense modifications.
Software
Added messages during calibration process
Added warm up and heater alarm messages
Added message “open loop” in mode current
Bug correction on tactile functionalities
6 Measurement and plots update July 08th,2021
Add noise plots measurement with PN9000 noise analyser instrument
- Calibrator_noise+10V.jpg- Calibrator_noise-10V.jpg
Discussion (11 comments)
Winne 1 year ago
First of all, I would like to agree with the statements of the previous speakers. This is really a great idea. And I can't wait to put the circuit into practice.
As we all know, the devil is in the details. I have a bit of a “stomach ache” with the relay, which is notorious for its contact resistances and thermocouples at low voltages and currents.
I understand the rationale for using the relay to switch between current and voltage mode. In both cases, the feedback loop compensates for the voltage drop in the DAC's 3.4 k output resistance caused by the AD8675's bias current. In voltage mode, the compensation loop is extended to the calibrator’s output which may cover adverse effects of the relay contact 5 to 6.
But in both cases, a relay contact / thermocouple (3-2 or 3-4) is also present in the feedback loop itself. I have less knowledge with signal relays in such niche applications. What is your experience with your calibrator? The relay is a non-latching type.
Do you have observed a voltage drift due to power dissipation in the relay coil after changing into the voltage mode?
Or do I overestimate the thermocouple effect of the relay compared with the overall uncertainty of the calibrator?
I would be grateful for any advice, including contributions from other readers.
Martin72 1 year ago
On the PCB and in the schematic there is a "battery boost option".
I didn´t find any other informations about.
Could you help me ?
RikV 2 years ago
Could you in some way publish the corresponding C-code?
sassa15 2 years ago
I am totally thrilled with your development. A brilliant design that leaves nothing to be desired. I immediately ordered the boards from JBPCB last week (delivery tomorrow) and started to procure the components at the same time. And now the drama begins.
I just managed to get hold of the display at RS-Online for 125 Euros. The new gen4 displays will not be available until 2023, so the display you used will only be available as a leftover. Farnell no longer has the relevant ICs from Analog Devices in its range. Here I found what I was looking for at Mouser. But the DAC alone costs over 100 euros. And now I'm thinking about whether this component will be the showstopper. This means that the total price of around 300 euros that you mentioned just under a year ago will be far exceeded. In addition, some components will not be available again until 2023. A request: What did you pay for the DAC at the time?
Many thanks for your answer and best regards
Martin
spo256al2 2 years ago
I am terrify by component price increasing, in my job it's the same nightmare. Everyday I have to fight with component unavaibility and price increasing.
I built two calibrators in 2021 and I paid display 92€ and 90€ for the DAC B version.
I am very happy about this calibrator and I often use it, the DAC is very good and the reference voltage too.
The only issu: the output amplifier doesn't like capacitive load, I knew this issu but to calibrate multimeter or oscilloscope, in my cases it was not a problem.
Do not hesitate contact me if you have a problem to build the calibrator
Vincent
sassa15 2 years ago
I already have two actual questions:
How are your experiences with the heating resistor on the heater because this is specified only up to 2W but is loaded with almost 2.5W.
You use the PTZ2222A on both boards. According to the BOMs but in different versions.
Heater: Nexperia PZT2222A,115
Calibrator: Onsemi PZT2222AT1G
Is there a special background for this?
Martin
spo256al2 2 years ago
At power startup:The PZT2222 drives the heater resistor and the VCEsat of the transistor is roughly 1V for 300-400mA, so the voltage in the resistor is 5V - VCEsat =>4V. This involves a maximum resistance power around 1.6W.
I didnot make difference between Heater and calibrator PZT2222A or 115.
Vincent
sassa15 2 years ago
since the calibrator will be a one-off for private use, I can live with the current price increase of about 25%. Much more dramatic, indeed existential, is the current supply and price situation for equipment manufacturers. However, the DAC is not available until Q1/2023 (probably). And how the price develops, you have to wait and see. I will now research every quarter whether the DAC is available. So, if problems arise I will get back to you in about a year. If I'm honest, I have projects that have been waiting longer to be completed.
Stay healthy.
Martin
spo256al2 2 years ago
You could use AD5781 it is pin compatible and software compatible exept 18bit resolution. May be less frustrating than wait Q1/2023.
Good luck and stay healthy
Vincent
xuelinAxiuyan 2 years ago
Do you sell manufactured goods？And how mach its price？
spo256al2 2 years ago
No, I do not sell this goods. I build this product to calibrate my TDS744A Tektronix oscilloscope. The BOM price is roughly 300€
Best Regards
Vincent
xuelinAxiuyan 2 years ago
Jouko
Jouko Koskinen 3 years ago
Interesting project.
Is it possible to order those PCBs from Elektor or some fab (existing project)?
BR,
Jouko
spo256al2 3 years ago
I just upload gerber files. So you can send these files to PCB maker company as Elektor pcb service or PCB-pool or JLPCB.
https://www.elektorpcbservice.com/
https://fr.beta-layout.com/pcb/
https://jlcpcb.com/
Rdgs
Vincent
Jouko Koskinen 3 years ago
Jouko
erayzor 3 years ago
I would like to propose Apex VRE305A (or VRE310 with 10V output) as an alternative voltage reference, having clearly superior specifications when compared to MAX6350. Especially the long-term drift (6 ppm/khr versus 30 ppm/khr) is much better, rendering a long-term burn-in obsolete. Due to the lower temperature drift (0.6 ppm/K versus 1 ppm/K), a temperature stabilization (i.e. an oven) may be unnecessary for many lab applications; e.g. a temperature range of 18°C to 28°C (20°C to 25°C) corresponds to a maximum change of 6 ppm (3 ppm). The initial accuracy (0.01 % versus 0.02%) is significantly better, too.
Regarding the amplifiers necessary to generate the +/-10.49V, I would like to recommend using resistor networks with very tight TC matching, e.g. LT5400A-1 (+/- 0.2 ppm/K typ., +/-1 ppm/K max.) instead of individual resistors having a TC of 2 ppm/K each (worst case matching +/- 4 ppm/K). Please note that the abolute resistance value (not the matching!) of such networks has quite loose tolerances (e.g. +/-7.5%).
One problem remains: Where do I get a DVM for the calibration of the calibrator having sufficient accuracy (i.e. much better than 0.001% or 10 ppm)? Or, alternatively, who can offer a good calibration service for the calibrator at reasonable costs?
spo256al2 3 years ago
I agree with you that Apex VRE305A has superior specifications compared to MAX6350. I designed this calibrator to calibrate my Tektronix TDS744 oscilloscope, so I have chosen MAX6350 for the price roughly 11€ versus 55€ for the VRE305 or LTZ1000. As my lab is in my cellar the temp can be cold as 15°C to 25°C, this is why I build the heater.
Regarding matching resistor LT5400A has better specifications than my two resistors. I agree.
Probably one day I will modify my calibrator with a better reference source and I will extend the voltage range to calibrate an old 5.5digit multimeter I have in my lab.
Concerning the calibration, may be you could have a friend with a 6.5digt DVM. From my side, a friend of mine has an Agilent 34401A with a up to date calibration certificate, from my side I have this same equipement too and a 7.5digits multimeter to compare and verify the calibrator.
If you can't find this DVM, you can send me the calibrator, I will calibrate it for free. You will pay just the shipping cost. Give me email adress.
Vincent
czecht@gmail.com 3 years ago
Are you working on revision for the PCB?
Thank you very much for your work!!!
Tony
spo256al2 3 years ago
The cost is arround 300€
The main component are the DAC and the tactile smart display.
Yes a PCB revision 1-3 is on line now. File name is calibrator_1-3
Rdgs
Vincent
czecht@gmail.com 3 years ago
Tony
Jürgen Kellers 3 years ago
spo256al2 3 years ago
The cost is arround 300€
The main component are the DAC and the tactile smart display.
Rdgs
Vincent
Jürgen Kellers 3 years ago
That's very reasonable for such a high-level design. Thanks alot for the very interesting posting!
Cheers
Jürgen
Johanan 3 years ago
spo256al2 3 years ago
R16 is 1kohm not 100ohm.(I will update this soon)
This 1k is used to obtain a voltage reference as near as +/- 10.48V. As the DAC is 20bit this gives a more accurate least step of 20uV for +/-10.48V
Regards
Vincent
Johanan 3 years ago
(I thought you may have some temp compensation trick which I don't know)
spo256al2 3 years ago
See picture.
I built a little PCB to ovenized the voltage reference circuit and I print a 3D enclosure to suround this. I am testing it in thermal chamber between 15°C to 30°C to measure the output drift. I will publish the result soon.
Vincent
closed-assembly.jpg (1060kb)
RoV 4 years ago
You say you measure temperature and you may compensate it in the future, but did you make at least a rough estimate of temperature drift?
Besides, I was wondering what is the warm-up time of the instrument before it reaches specs.
Thank you for the post,
Roberto
spo256al2 4 years ago
I plan to use a climatic chamber to measure the output drift from 10°C to 30°C and add correction factors.
I will build another calibrator to compare the output drift in the 10°C to 30°C on both calibrator
I measured, less than 3min to reach less than 10ppm accuracy.
Rdgs
Vincent