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project snapshot:
		Development of an automotive on-board diagnostic sensor prototype for monitoring the presence of a catalytic radiator coating
	BACKGROUND	We were approached by a multi-national materials company to develop a prototype sensor for use in cars and trucks.  The company had developed a proprietary catalyst which was being applied as a coating to engine radiators in a certain make of automobiles.  They now needed to develop a sensor technology which could be incorporated into the engine compartment to continuously monitor the presence of the coating over the course of the lifetime of the vehicle.  The coating material safely converted the low levels of the pollutant gas ozone to oxygen, thus reducing the net impact on air pollution or net effective emissions of the vehicle.
	PROBLEM	Above all, the sensor needed to be designed such that it would be intrinsically rugged and reliable to a degree that individual production units could typically be expected to endure the full range of under-hood environmental stresses of heat, moisture, dirt and vibration over the course of however long the vehicle remained in service, which was assumed to be typically seven years.   The sensor should also be preferably small, easy to install with a low manufacturing cost in automotive volumes.  The client had a mild preference for a non-contact sensing solution.  However, beyond that the technical options were open and continuous monitoring versus intermittent monitoring was also not an issue.  For instance, we were told that if it made the development simpler then it would also be quite acceptable for the sensor to perform a single measurement only once whenever the engine was first switched on.  This was because the rate of deterioration of the coating was, at least, extremely slow.  The deliverable for the project would be a fully documented and operational prototype which was to be installed in a test vehicle supplied to us by the client and then subjected to a long-term test by the client.
	SOLUTION		During the initial phase of the project we considered a number of technical alternatives and finally settled on an IR based, reflectance sensing approach.  A bread board prototype was designed and assembled and tested in the laboratory using customer supplied samples of radiators having various degrees of coating present.  The optical reflectance of the radiator samples, (an unusual surface) were characterised. The optoelectronics were sourced from a high volume optoelectronics supplier who was accustomed to supplying the automotive market.  From there we progressed to engineering a practical arrangement for the functional model. The basic science of the sensor was conceptually straightforward.  However, a series of application specific issues needed to be addressed in order to properly develop a practical, rugged and reliable sensor.  This meant adding features to cope with the harsh environmental extremes: § Operating temperatures from sub-zero (for example Alaskan winter) to high (for example summer / hot climate / hot or overheated engine). § Variable and potentially high shock and vibration levels. § Variable moisture levels / must withstand being drenched in water. § Potentially dusty and dirty extending to desert like conditions and potentially abrasive environments. § Variable background light levels; (night/day). § Electrically noisy environment, (EMI, etc.).
			The sensor housing was machined from aluminum and anodized.  It houses a near IR (890nm peak) source, two detectors, fused silica optical windows and a preamplifier.  We extensively tested the operating temperature range over more than a 100C range in controlled environment lab tests and determined a reliable maximum operating temperature. (The minimum was never reached.)  We subsequently included a temperature sensor and an automatic sensor signal over-temperature lock-out.  Another issue was variable stray light. We used various techniques to eliminate sensitivity to background light, including pulse modulation and sensor signal saturation detection.  Sensitivity to dirt and frost accumulation on the optical windows and source intensity variations was reduced to essentially zero by a proprietary, optical self-referencing design.
				Prior to installation the sensor module was potted using a special automotive quality potting compound.  This is a standard procedure for rendering automotive electronics moisture and vibration resistant.  However, it was a tense process for us.  You only get one chance at getting it right.
				It was also feasible, although typically unlikely, that extreme amounts of dirt/mud/debris could accumulate on the optical windows. So we also incorporated a low/no signal lock-out and warning.  The vehicle owner could then simply hose off the sensor at their convenience to remedy the problem.
				The small signal processing unit is mounted beneath the dash. [in the final production model all the signal processing functions were, instead, to be integrated into the vehicles electronics system]
		The prototype functioned at least according to design requirements and beyond our expectations in terms of signal stability under all sorts of conditions. We never did determine the time to failure of the prototype.  However, with the single exception of the test vehicle, if you go looking under the hood of your own car for a radiator coating OBD, you will not find one!  Following the conclusion of the project our client determined that a coating presence OBD would not be an industry requirement.
	SRC TEAM	Myself:  Team leader. Sensor design; laboratory experiments; pre-delivery road test. Mechanical engineer – sensor housing design Mechanical designer – mechanical drawings Machinist Electronics engineer – circuit design Electronics technician – circuit assembly. Lab assistant – mechanical assembly; potting of the sensor module and purchasing agent
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