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Sensor failure detection

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electronicsman

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In my circuit i need to have sensor failure detection for example temperature sensor. For this i need to buy a sensor which supports a failure detection on its own or what is the circuit i need to build around it to detect this sensor failure? Please advise.
 

Its depends on the type of sensors. RTD and thermistors are easy to identify the sensor failure. Select any specific type of sensors based on your application and requirement, so that we can help to give you the solution.

Udhay
 

you could program an Arduino that will read the signals of temperature... if the temperature all the sudden goes erratic, then maybe something is going wrong with it and you could program Arduino to tell you if temperature made a big drastic change. Idk, just an answer, this is my first answer btw.
 

But how does the sensor by itself know it has failed?
 

But how does the sensor by itself know it has failed?

Only a full read of the datasheet for the sensor in question can answer that... if it is a sensor with inbuilt failure detection...

If I couldn't find an off-the-shelf IC that does the above, I'd scavenge datasheets and app notes for some of the ideas for e.g. regulators and converters and their assorted internal protection circuitry.

There must be a max-min signal range for every sensor IC. You said temperature sensor. If a minimum (and/or maximum) e.g. voltage is known and expected from the temp sensor, anything outside that may denote a fault: a window comparator circuit or two comparators could notify of any voltage excursions below or above expected functioning range to trigger an LED or a shutdown or whatever should happen.
 

Hi,

You really need to define your sensor, it's function, it's interface, power supply...and what you mean with "know by itself".
Detecting is only one part.... you additionally need to define how to show the failure. An LED?

****

A simple case could be an RTD. Two wires.
And as failure indicator a LED.
For a valid measurement there needs to be a valid voltage across the RTD. If you know the measurement current you may specify the valid voltage range. If the voltage across the RTD is beyond this range there will be a failure.
For sure you may use a window comparator to detect the error state. It needs extra circuitry and an extra power supply.

But what do you gain by this?
The simple two wire sensor becomes more complicated, more expensive, it needs maintenance(battery)....
And - because the failure detect circuit is more complex as the sensor itself - it is more likely that the detector circuit fails than the sensor circuit.

Thus often it makes more sense to build a simple sensor and place the failure detection to the measurement unit.
Then the sensor itself will not detect any failure.

*****
"Sensor" is a huge range. It may be an RTD...it may be an image generating ultrasonic sensor for medical applications...and a millon others.

Klaus
 
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    d123

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Failure for RTD usually means open or short, thermo couple amplifier can detect open circuit only. Detecting implausible temperature values or t.v.-changes might work in special situations, but isn't a commonly applied method.
 

In my circuit i need to have sensor failure detection for example temperature sensor. For this i need to buy a sensor which supports a failure detection on its own or what is the circuit i need to build around it to detect this sensor failure? Please advise.

You can provide the firmware with an intelligence in order to check for prohibited conditions, such as the sensor operating outside the expected range. Another often preferred approach in such cases is to create an interface with a current loop, such as the industrial sensors 4mA ... 20mA. This actually creates a third state, for example 4mA being the logic `0` level, 20mA the logic level `1` and the lack of current (0 mA) as the `disconnected` state.
 

Unfortunately or forunately i am in the field of Automotive. So i need to be compliant with several standards.
 

But how does the sensor by itself know it has failed?

Sensors we can divide in to two types : Semiconductor (Active type) or Transducer (Passive type). Sensor has no brain to detect the failure by itself but the sensing circuit has. Except that if the semiconductor type sensor has some failure alert pin, we can't predict the sensor failure. Even if the sensor has alert pin, we can't use it while total chip(sensor) failure condition. This semiconductor sensors will not be a rugged type (for automotive) and the measurement temperature range will be limited to certain level.

Failures can be two types : open circuit (may be due to sensor failure or wire connectivity failure) & short circuit (mostly due to terminal short circuit). This two applicable only for transducer type. This failure can be identified by measuring out of range output voltage and is totally depends on the type of sensors and the type of signal conditioning circuit.

Udhay
 

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