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Old 1st March 2014, 18:30   #1
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Default Calibration of Sensors used in cars?

Hello BHP'ians,

I am posting a thread here to understand the sensors used in a car that gives various data and helps the car run normally as prescribed.

I wanted to know the frequency of calibration need for these sensors if at all they are needed to be calibrated.

I am asking this noob doubt because, I work in a food industry where temperature and pressure sensors are VERY important to the process which yields SAFE food produced. We rely a lot on these sensors and probes placed in the equipment used to manufacture products for consumption.

The temperature sensors, pressure sensors, DPT (differential pressure), pressure gauges are all having a strict internal and external calibration process. The internal calibration is done every month and external one is done by a NABL laboratory every year as this is one main criteria to get the FSSAI (Food Safety Standards Authority of India) licence for manufacturing.

If one of these sensors/probes/gauges go wary we end up in huge losses so what is the status if looked at automobiles?

There are many sensors used by the ECU to transit/receive data to according programme the car to run efficiently and smoothly. How does one know the sensor condition and is not required to calibrate them? Just changing oils and filter do the trick?

Googling and using Wikipedia the list of sensors used are as follows:
  • Air–fuel ratio meter:
  • Crankshaft position sensor:
  • Engine coolant temperature sensor: used to measure the engine temperature
  • MAP sensor: Manifold Absolute Pressure, used in regulating fuel metering.
  • Mass flow sensor: or mass airflow (MAF) sensor, used to tell the ECU the mass of air entering the engine
  • Oxygen sensor: used to monitor the amount of oxygen in the exhaust
  • Speedometer: used measure the instantaneous speed of a land vehicle
  • Throttle position sensor: used to monitor the position of the throttle in an internal combustion engine
  • Tire-pressure monitoring sensor: used to monitor the air pressure inside the tires
  • Torque sensor: or torque transducer or torque meter measures torque (twisting force) on a rotating system.
  • Transmission fluid temperature sensor: used to measure the temperature of the transmission fluid
  • Water sensor or water-in-fuel sensor: used to indicate the presence of water in fuel
  • Wheel speed sensor: used for reading the speed of a vehicle's wheel rotation

There will be more sensors but the list I have given above is just an example. Attaching a few more screen shots of the list of sensors used in a vehicle.

Calibration of Sensors used in cars?-sensors.jpg

Calibration of Sensors used in cars?-sensors1.jpg

Calibration of Sensors used in cars?-untitled.jpg

SOURCE: http://en.wikipedia.org/wiki/List_of...transportation

http://www.idc-online.com/technical_...iveSensors.pdf

Can someone clear up my doubts?!

Thanks,
Anurag.

Last edited by a4anurag : 1st March 2014 at 18:31.
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Old 5th March 2014, 13:00   #2
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Default Re: Calibration of Sensors used in cars?

Thread moved from the Assembly Line (The "Assembly Line" Forum section) to Technical Stuff. Thanks for sharing!
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Old 5th March 2014, 14:10   #3
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Default Re: Calibration of Sensors used in cars?

Quote:
Originally Posted by a4anurag View Post
Hello BHP'ians,

I wanted to know the frequency of calibration need for these sensors if at all they are needed to be calibrated.
No, the automotive sensors don't need any calibration.

The digital sensors ( e.g. speed sensors ) will not drift - they are designed to work lifetime of the car e.g. 15 years. In case they fail, the ECU will recognize the absence of the signal and will report the appropriate malfunction code.

There are sophisticated software algorithms to compensate for the drift in analogue sensors and it is done automatically by ECU. If the drift is outside permissible limit, again malfunction code is reported.

So all in all, you need not worry about recalibration.

The ECU software is quite advanced and emission regulations place very stringent requirements to identify and report the faulty sensors.

Some of the ECU algorithms are adaptive e.g. gear-shift in automatic transmission. The learned values can be reset by typically removing battery supply for 10 minutes.
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Old 5th March 2014, 14:14   #4
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Default Re: Calibration of Sensors used in cars?

Quote:
Originally Posted by a4anurag View Post
I wanted to know the frequency of calibration need for these sensors if at all they are needed to be calibrated.

There are many sensors used by the ECU to transit/receive data to according programme the car to run efficiently and smoothly. How does one know the sensor condition and is not required to calibrate them? Just changing oils and filter do the trick?
Hi Anurag

As you listed down, there are numerous sensors in a new generation automobile which gives inputs to the different ECUs.

Since I work on brake systems, I can list the example of few of the sensors used in ABS / ESC.

(1) Wheel speed sensors - do not require any calibration. They work on simple electromagnetic induction principle and sense the wheel speeds within a specified range. They do not lose their calibration even when the battery / dome fuse is disconnected.

(2) Steering angle sensor - this is used in cars equipped with Electronic Stability Control (ESC) for measuring the steering angle. In vehicle assembly lines, there is a station where the straight-ahead position of the steering wheel is set and the steering angle sensor 'zero' position is calibrated. Unless one disconnects the battery / removes the dome fuse (which happens during long duration shipment to overseas locations), the sensor retains the zero position.

In case the power is disconnected, there is a simple procedure given in the Owner's Manual for recalibration of the steering angle sensor by driving forward in the straight ahead position for so many seconds / so much distance (slightly varies across OEMs).

In my opinion, all the sensors in a vehicle either do not require calibration, or once calibrated, do not require recalibration.

In case a sensor loses calibration (cannot see how, unless it is damaged), there will definitely a tell-tale in the cluster denoting a malfunction (of the system, for e.g. MAP sensor malfunction will throw up Engine Malfunction lamp).

A diagnostic tester will show which sensor is malfunctioning.

Hope this answers your question, at least partially!

Regards
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Old 5th March 2014, 14:59   #5
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Lightbulb Re: Calibration of Sensors used in cars?

The sensors used in the automobiles IMO are use and throw type sensors. These sensors come factory calibrated to the desired requirement of the car manufacturers. Any fault or malfunction in such sensors are directly replaced with spares one. Also such sensors dont have any provisions to be calibrated as most of them are mounted on the body and removing them for calibration will do more damage than required based on their shapes and sizes.
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Old 9th March 2014, 18:59   #6
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Things in my head are clear now as I knew my doubts will get an answer here.

Thanks guys and Thanks T-BHP.

Anurag.
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