Abstract: An apparatus for monitoring the exhaust of an engine includes a flow-through chamber for receiving exhaust, a source of electromagnetic radiation and a detector. The source provides electromagnetic radiation in a range comprising the infrared, visible and ultraviolet wavelengths. The source and a detector are arranged so that radiation passing through the chamber is incident on the detector. An electronic circuit is connected to the detector to provide a signal indicative of the attenuation of the radiation by particles in the exhaust in the chamber. The detector provides respective measures of radiation which it receives for at least two different wavelengths of the radiation, and the electronic circuit provides corresponding electrical signals indicating the attenuation of the two different wavelengths by particles within the exhaust in the chamber. The wavelengths are selected to be those for which the attenuation caused by nitrogen dioxide in the exhaust is substantially the same.

Abstract: A wheel chair motor control circuit for a wheel chair having two independently controllable motor-driven wheels. The user has a "joystick" control operable from a datum position to move the wipers of two potentiometers both independently and simultaneously from their corresponding datum positions. A first, proportional control circuit is provided for each motor to supply it with drive power proportional to the magnitude of the deviation of its corresponding potentiometer wiper from datum and a second reversing circuit is provided for each motor to operate a reversing relay connected thereto in accordance to the direction of the deviation of its corresponding potentiometer wiper.