Should you have a requirement for non contact temp
sensing Melexis and TI offer IR T sensors -
These tend to be more expensive soplutions, however.
I did have a look at the links and from the block diagram in the link - http://www.cypress.com/?rID=61127, it is clear that we can use different types of temperature sensors, but the criteria for the selecting the sensor is not mentioned there. Could you give me some pointers as to how we can select the sensor?
I am pretty new to this domain and am still doing a feasibility study therefore any sort of information would be useful.
I am not veryx experienced with Temperature sensors (programming is my main-task). As far as I know:
Thermocouples are best for higher temperatures, inherently precise, the signal has a low amplitude (V/degree) could be noisy due to the needed amplification.
PTCs and NTCs are cheap but unprecise and need calibration, are aging, but are usefull within your estimated temperature range. Repeated calibration needs some software and hardware and regular checking.
Measuring precisely the junction temperature can be made, but ther is one thing I find disturbing: the large (for electronic equipment) distance between the measurement point(s) and the device to set / control the required temperature.
So I would suggest a complete different solution: Use a (or more) thermo-sensor(s) with I2C interface at lower frequency (shielded cabling) and connect it to a PSoC with an LCD and a keypad. A simple proof-of-concept can be made easily with a cheap PSoC1 development board.
The range of measurement will be low for this application. Thermistor would be a good choice.
How is the mechanical setup -
1. where will be the sensors and actuators positioned?
2. where will be PSoC located?
Since this is a food/trucking application, one of the easiest and inherently
linear would be an LM334/335 type sensor. The LM334 is a current sensor,
can be used over long cable runs being a current device, and with a resistor
to convert I to V, and PSOC A/D, and a simple equation to calculate T, its
trivial to implement. Very linear, and initial uncalibrated accuracy of +/- 3
degrees C and low cost from LTC. The 335 is a V type sensor, so more
appropriate for shorter distances. .5 C initial accuracy part is AD592 from
analog devices, a current part.
Of course diode is the cheapest sensor http://www.ti.com/lit/an/sboa019/sboa019.pdf
Go to ti for a borad selection of sensors. http://www.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=611&uiTemplateId=NODE_STRY_PGE_T
Then there is always integrationg into vehicle system, via CAN, LIN....
Then there is a plethora of serial buss parts, cabling adding cost to handle
high noise environment.
Yes, the answer seems to be as usual: "That depends on..."
The temperature range
Ease of use
Really appreciate your help in providing answers. The sensors suggested, reading material links are really useful.
Bob, here are the few specifications
Here is a guide that might help. Current sensor probably best approach,
save Cu costs, 2 wire, handle long distances. You would have to do simple
computation of compliance V for the sensor.
There are several guides here, including an automotive solutions guide -
Thanks to all for providing me with a lot of useful information.