[Diy_efi] Temperature/Pressure sensors

[Torbjörn Forsman]

The LM335 and most other IC temperature sensors (there are also some 
with digital interface, for example I2C) have a reputation for bad 
reliability in the field, especially in severe environments as in 
vehicle engine compartments, heavy industry etc. There are good reasons 
why all mass produced engine management systems still use NTC or nickel 
resistance (PTC) temperature sensors instead.



For the most common NTC sensors, there are just three basic types to 
take care of.

The "Bosch" temperature sensor, also used by many other japanese and 
european manufacturers, has a characteristic which is to be found here:
http://www.epcos.com/inf/50/db/ntc_06/LeadlessDisks__B57220__K220.pdf

GM's standard sensor, used for many years on their C3 and P4 systems has 
this characteristic:
http://www.epcos.com/inf/50/db/ntc_06/Leaded__NTC__B57962__S962.pdf

Ford uses NTC temperature sensors with a resistance about 33 kohm at +25 
?C. I haven't found any good documentation on those.

Characteristics for nickel PTC sensors (seldomly found, mostly on french 
and japanese systems) can be found here:
http://www.oiml.org/publications/R/R084-e03.pdf


When calculating the temperature - voltage graph, one must know the 
resistance of the pull-up resistor in the ECU as well as the supply 
voltage (almost always 5 V) and if there is any resistor in parallel to 
the sensor. This has to be done by reverse engineering the ECUs.

Bosch typically uses either 1,0 kohm, 2,7 kohm or 2,87 kohm pull-up in 
their Motronic and (digital) Jetronic ECUs. Ignition ECUs (EZ) as well 
as the analog L-jetronic, LE-, LU- and KE- ECUs have completely 
unstandardized pull-up resistors. In some ECUs with 2,7 or 2,87 kohm 
pull-up there may be a parallel resistor.

Japanse ECUs typically have 2,7 kohm pull-up, no parallel resistor.

GM uses 1,0 kohm or 348 ohms pull-up, no parallel resistor. In some 
cases, there are two different pull-up resistors (one 348 ohms and one 
in the 3 kohm range) that can be switched under software control to 
increase the measurement range.

Best regards

Torbj?rn Forsman


Carter Shore wrote:
> Check out National Semiconductor,
> LM335 yields 10mV/degree K.
> Cheap, tiny, easy to interface.
> 
> Carter
> 
> --- Alex Garbino <agarbino at gmail.com> wrote:
> 
> 
>>Hello,
>>
>>I'm trying to build a data acquisition system to
>>monitor various
>>temperatures and pressures. I've been looking at
>>thermocouples, RTDs, and
>>thermistors; but they have widely different
>>advatnages and disadvantages. I
>>was thinking of using thermistors to monitor air
>>intake temperature &
>>pressure (on a turbocharged car, so I would like to
>>monitor atmospheric,
>>pre-intercooler, and post-intercooler/manifold) as
>>well as coolant temp, oil
>>pressure & temp, and EGTs, both before and after the
>>turbocharger.
>>Thermistors seem the best choice for air intake,
>>since they have a fast
>>response and are cheap; however, I cannot find good
>>datasheets regarding the
>>linearization coefficients.
>>
>>Does anyone have advice on a good way to capture
>>data, as well as any tips
>>on the best way to mount these sensors (a modular
>>system would be best, so I
>>could move sensors to different positions and switch
>>them in and out with
>>minimum hassle)? Also, can anyone recommend a good
>>source of cheap sensors?
>>
>>The signals will be captured via a PIC18F series'
>>A/D converters/digital
>>inputs, and relayed immediately onto an on-board
>>computer. Please let me
>>know of any resources that would be helpful!
>>
>>Regards,
>>Alex
>>
>>For a more detailed discussion on what I'm trying to
>>achieve, please see
>>http://www.mkiiitech.com/forums/viewtopic.php?t=903
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> 
> 
> 
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