Author Topic: How to adjust the zero position of the gasflow analyzer  (Read 615 times)

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Offline daisizhou

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How to adjust the zero position of the gasflow analyzer
« on: June 12, 2021, 04:21:07 am »
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 2.512V

SZ75434---LOW PRESSURE
ASCX100DN-----HIGH PRESSURE
ASCX15AN------barometric pressure

If you know how to adjust please let me know, thanks
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Online AndyC_772

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #1 on: June 12, 2021, 05:43:47 am »
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.

Offline daisizhou

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #2 on: June 12, 2021, 10:44:59 am »
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 calibrated
I don’t know how to calibrate, please let me know if you know
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Offline TheMG

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #3 on: June 12, 2021, 06:26:12 pm »
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.
« Last Edit: June 12, 2021, 06:27:54 pm by TheMG »
 

Offline voltsandjolts

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #4 on: June 12, 2021, 07:06:08 pm »
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
 

Offline TheMG

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #5 on: June 12, 2021, 10:20:43 pm »
Page 11:

Quote
Certification

Allied Healthcare Products, Inc. tests, inspects and certifies each instrument before it is shipped from the factory. Enclosed are the results of these tests.

For continued reliable operation, Allied Healthcare Products, lnc. recommends annual certification of the RespiCal Calibration Analyzer. To return a RespiCal Calibration Analyzer to Allied Healthcare Products, Inc. For certification or factory service, follow the procedures in section"Claims and Return lnformation"

They 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.
 

Offline daisizhou

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #6 on: June 12, 2021, 11:17:27 pm »
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 here
Other chips are logic processing or operational amplifier chips
I found the definition of pressure sensor, 3-pin voltage output
« Last Edit: June 13, 2021, 12:32:41 am by daisizhou »
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Offline daisizhou

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #7 on: June 12, 2021, 11:53:35 pm »
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
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Offline amyk

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #8 on: June 13, 2021, 12:33:04 am »
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.
 

Offline daisizhou

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #9 on: June 13, 2021, 04:24:25 am »
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 me
I tried to connect the serial port at the end of T300 with windows hyper terminal, the screen is as follows
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Offline daisizhou

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #10 on: June 13, 2021, 04:25:29 pm »
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 why
Low pressure can reach as low as -128.05cmh2o,I think this is normal
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Offline amyk

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #11 on: June 13, 2021, 11:44:11 pm »
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.
 

Offline daisizhou

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #12 on: June 14, 2021, 03:20:47 am »
OK ,The following attachments are the main system ROM and configuration ROM

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Offline daisizhou

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #13 on: June 14, 2021, 03:54:15 am »
I suspect there is a problem with the pressure sensor,So I separated the pressure sensor from the original circuit

The 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
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Offline daisizhou

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #14 on: June 14, 2021, 04:07:56 am »
I return the sensor to the circuit and measure VOUT online
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Offline daisizhou

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Re: How to adjust the zero position of the gasflow analyzer
« Reply #15 on: June 14, 2021, 02:16:14 pm »
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
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