AN759| Application Note
Maxim/Dallas > App Notes > AUTOMOTIVE
SENSOR SIGNAL CONDITIONERS
Keywords: self diagnostics, system diagnostics, auto-zero, output drift, high performance signal conditioner, low cost signal conditioner, MAX1457, MAX1478, MAX1452, MAX1455, MAX1463, signal conditioners conditioning
Jun 18, 2001
APPLICATION NOTE 759
Adding Diagnostic Capability to MAX14XX Low Cost High Performance Signal-Conditioning Devices
A cost-effective procedure for adding system diagnostic, product diagnostic, output drift check, auto-zeroing capability, etc., to your products which are based on the MAX1478, MAX1452, MAX1455, MAX1457, and MAX1463 family of high-performance signal conditioning products without changing the test system or adding significant time to the calibration process. This approach takes advantage of built-in nonvolatile flash memory included in these low-cost signal conditioners. The concept is implemented by making an accurate measurement of the output voltage at predefined reference conditions and storing it in the flash memory for future reference. This application note describes a simple and cost-effective procedure for adding diagnostic checks to determine product functionality and sensor output drift. This enhancement can be added to any MAX14XX device with nonvolatile memory without changing the test system or adding significant time to the calibration operation. MAX14XX signal-conditioning devices are generall
y used in conjunction with pressure sensors to correct their inherently large temperature error. Although the same principle applies to other types of sensors, this document refers solely to pressure-sensor applications for the sake of simplicity.
Benefits of Adding Diagnostic Capability
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Checking the functionality of the signal-conditioning device. Indicating the level of error after calibration. Indicating drift in the sensor output. This is desirable especially in the case of absolute-pressure sensors, because loss of reference vacuum can cause output drift, which may not be easily detectable after calibration. Verifying proper functioning and troubleshooting the test system. Changes in output voltage in the reference condition could provide hints of inaccurate pressure setting, incorrect VDD, malfunctioning ASIC, etc.
Overview
Maxim's MAX14XX series of smart signal-conditioning products include nonvolatile memory that can be used to store product-run information and calibration values. Once the device is calibrated, the output voltage (Vcal) of the device should be measured under reference conditions and the value of Vcal written to memory. Reference temperature and pressure conditions should be chosen to minimize the influence of the test system on the reference conditions. For gage-pressure devices, reference conditions are usually room temperature and atmospheric pressure. For highly accurate products, room temperature may need to be controlled and atmospheric pressure measured independently. When it comes to absolute-pressure sensors, a repeatable reference pressure must be chosen (it may not be atmospheric pressure).
Reference Temperature
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