How to adjust the zero position of the gasflow analyzer - Page 1
Forum section: electronics / projects

author: daisizhou
author_rank: Super Contributor
timestamp: June 12, 2021, 04:21:07 am
content: Gasflow analyzer Respical T300，the boot test is normal。But the display value cannot show the zero position.I plan to try to repair,I did not find the adjustable resistor (potentiometer) on the circuit board.Test the output voltage of the pressure sensor, the voltage will change according to the pressure value.The model of the sensor is ASCX15AN, ASCX100DN, SZ75434。normal air--ASCX15AN output 4.561V , ASCX100DN output 0.251V, SZ75434 output 2.512VSZ75434---LOW PRESSUREASCX100DN-----HIGH PRESSUREASCX15AN------barometric pressureIf you know how to adjust please let me know, thanks

author: AndyC_772
author_rank: Super Contributor
timestamp: June 12, 2021, 05:43:47 am
content: How old is it? That Dallas SRAM module may have a dead battery by now, in which case any calibration constants will have been lost, and you may be out of luck.

author: daisizhou
author_rank: Super Contributor
timestamp: June 12, 2021, 10:44:59 am
content: Yes, I noticed this Dallas battery problem.I am trying to calibrate it, but I did not find an adjustable resistor or other electronic components that can be calibratedI don’t know how to calibrate, please let me know if you know

author: TheMG
author_rank: Frequent Contributor
timestamp: June 12, 2021, 06:26:12 pm
content: It's more than likely calibrated digitally, which is why you can't find any pots to adjust on the board. It will be done either through calibration menus on the front panel, or may require connection to a PC.This means you will need to find a manual with the calibration instructions. Without that information, you're basically out of luck.

author: voltsandjolts
author_rank: Unknown
timestamp: June 12, 2021, 07:06:08 pm
content: The manual doesn't mention calibration, which might be a good thing, maybe it's simple.I was expecting a note saying 'return for calibration'.Manual too big for forum even after compression, so here's a link:Allied-RespiCal-T300-Respiration-Analyzer-User-manual.pdf

author: TheMG
author_rank: Frequent Contributor
timestamp: June 12, 2021, 10:20:43 pm
content: Page 11:QuoteThey use the word "certification" rather than "calibration", but essentially the same thing. So it looks like they intend for the unit to be shipped to the manufacturer for calibration and any repairs. As such, it's very likely only the manufacturer has the procedures (and software if applicable) necessary to perform a calibration.

author: daisizhou
author_rank: Super Contributor
timestamp: June 12, 2021, 11:17:27 pm
content: I have read the operating manual,But I did not find the service manual or maintenance and calibration manual.I check the circuit board PCB,Found that the core MCU is DS80C310 microcontroller,AT27C512R is a one-time write to EEPROM,I think the main program should be stored in AT27C512R,Because DS80C310 has no storage function.dallas DS1644-120 should be SDRAM and battery maintenance chip,May be duration statistics or timing。There is also a readable and writable EEPROM 24LC32A,I guess the configuration or calibration data may be stored hereOther chips are logic processing or operational amplifier chipsI found the definition of pressure sensor, 3-pin voltage output

author: daisizhou
author_rank: Super Contributor
timestamp: June 12, 2021, 11:53:35 pm
content: After reading the contents of AT27C512R and 24LC32A, I still can't understand it. The front part of 24LC32A is the boot content.If you have better suggestions, welcome to provide

author: amyk
author_rank: Super Contributor
timestamp: June 13, 2021, 12:33:04 am
content: You're going to have to do some reverse-engineering to figure out how it's calibrated. Given that it's a pretty well-known MCU with no readout protection and the code is in a separate ROM, it shouldn't be too difficult. I'd start by figuring out the address/data mapping and loading the ROM image in a disassembler. The first three bytes of the ROM are LJMP 0C3E3h which makes sense for a first instruction.

author: daisizhou
author_rank: Super Contributor
timestamp: June 13, 2021, 04:24:25 am
content: Sorry, I am not familiar with disassembly,Familiar with the hardware circuit, very confused about the software part.If you need hardware circuit analysis, I can try to draw a schematic diagram.If you want to analyze the program, I hope good people can help meI tried to connect the serial port at the end of T300 with windows hyper terminal, the screen is as follows

author: daisizhou
author_rank: Super Contributor
timestamp: June 13, 2021, 04:25:29 pm
content: I checked the data sheet of the sensor,VCC is 5V power supply,vout is the analog output voltage.For example,0 cmh2o=2.92v,10cmh2o=3.15v,20cmh2o=3.38v,30cmh2o=3.61v.........0.2xV voltage increase.The highest I chose 4.92V, the pressure reached 85.07cmh2o.But the low pressure range can only reach 85.07cmh2o，The instructions say that it can reach +-120cmh20,I do not know whyLow pressure can reach as low as -128.05cmh2o,I think this is normal

author: amyk
author_rank: Super Contributor
timestamp: June 13, 2021, 11:44:11 pm
content: Are you saying the sensor works or not?If you post the main ROM, we can take a look and see how it can get into calibration mode.

author: daisizhou
author_rank: Super Contributor
timestamp: June 14, 2021, 03:20:47 am
content: OK ,The following attachments are the main system ROM and configuration ROM

author: daisizhou
author_rank: Super Contributor
timestamp: June 14, 2021, 03:54:15 am
content: I suspect there is a problem with the pressure sensor,So I separated the pressure sensor from the original circuitThe following is my test process:In the original circuit,Sensor 2 pin is the power supply,3 pin is voltage output,Pin 4 and Pin 5 are negative,Finally, I independently provided a set of voltage sources,I observe the pressure value displayed on the screen and adjust the corresponding voltage value,Finally I got a data table of voltage value corresponding to pressure value

author: daisizhou
author_rank: Super Contributor
timestamp: June 14, 2021, 04:07:56 am
content: I return the sensor to the circuit and measure VOUT online

author: daisizhou
author_rank: Super Contributor
timestamp: June 14, 2021, 02:16:14 pm
content: Looking forward to your analysis results,Thank you for your help,Sensor is good,Linear change in pressure range。The most important thing now is how to calibrate

author: amyk
author_rank: Super Contributor
timestamp: October 03, 2021, 04:40:07 am
content: I have worked with the OP to figure out how the calibration constants are stored in the EEPROM and how they are used. Here is a summary, see attached for detailed notes.Code:High pressure:0170 ADC value at 0 PSI0172 ADC value at 100 PSILow pressure:0194 ADC value at 0cmH2O0196 ADC value at 120cmH2O019a ADC value at -120cmH2OBarometer:0230 ADC value at 10.000inHg0232 ADC value at 29.920inHgAll values are in 16-bit BE. The above sensors are all linear.High flow:0110 ADC value at 0LPM0112 ADC value at 240LPMThe sensor is a hot-wire anemometer and its response is nonlinear.Piecewise linear interpolation is used with a linearisation table at 0400-05ff.This is a 256-entry table of values in units of 8192nds of the total output range (0-240000, units of 0.001LPM). See the notes for more detail.Low flow:0136 ADC value at 0LPM0138 ADC value at 25LPMThe sensor is a hot-wire anemometer and its response is nonlinear.Piecewise linear interpolation is used with a linearisation table at 0600-07ff.This is a 256-entry table of values in units of 8192nds of the total output range (0-25000, units of 0.001LPM). See the notes for more detail.

author: nguyenphong
author_rank: Newbie
timestamp: March 27, 2024, 09:06:37 am
content: I also need to calibrate T300 . can you help me how to

author: daisizhou
author_rank: Super Contributor
timestamp: March 28, 2024, 01:16:09 am
content: OK, can you tell me the current status of your T300?

author: nguyenphong
author_rank: Newbie
timestamp: March 28, 2024, 01:51:14 am
content: it displayed "calibration has expired" and the low pressure displayed not zero value!

author: daisizhou
author_rank: Super Contributor
timestamp: March 28, 2024, 02:48:50 am
content: "Calibration expired"--you need to read the DS1644-120 internal data,Then modify the calibration date, and finally rewrite the data to DS1644-120,Calibration has expired before normal display can be restored."Low pressure display -0.93 bar"---First you need to read U8(24LC32A),It is a 4KB bin file,All calibration data is stored inside this EEPROM chip,After reading the complete data, you need to prepare a digital pressure gauge,I choose druck-DPI705(You can also choose other similar models),Then refer to "amyk"'s post.If you still don’t understand, you can contact me(daisizhou#sina.com #->@)I wish you success, I am a biomedical engineer,Looking forward to communicating with youBy the way, there is also a calibration firmware, I can send it to you if you need it

author: nguyenphong
author_rank: Newbie
timestamp: March 28, 2024, 04:34:59 am
content: I tried to connect by hyper terminal but not successful. Has you got any advice?

author: nguyenphong
author_rank: Newbie
timestamp: March 28, 2024, 05:09:14 am
content: I'm biomedical engineer. Would you send me calibration firmware and how to use it. Thank you very much.

author: daisizhou
author_rank: Super Contributor
timestamp: March 28, 2024, 05:20:28 am
content: For the programmer I use labtool-48xp (more expensive) or CH341A (cheap)--<DS1644-120 is not supported>Do you have online software for T300?

author: daisizhou
author_rank: Super Contributor
timestamp: March 28, 2024, 05:41:14 am
content: How to contact you? your email address?

author: daisizhou
author_rank: Super Contributor
timestamp: August 28, 2024, 12:15:10 pm
content: I spent some time today updating the original yellow green backlit LCD screen。The new LCD screen has a white backlight, which looks very clear.Share with friends who are still using it, thank you