Abstract: Method and apparatus for precisely mixing gases in which solenoid valves sequentially feed separate gases to be mixed to a common pressure regulator and flowmeter.

Abstract: A laboratory incubator or similar electronically-controlled piece of hardware, is provided with at least one modular control unit, e.g. one for setting a desired relative humidity, and for indicating the actual relative humidity being attained within the laboratory incubator or similar device. The or each control module is provided with a normally hidden switch which may be changed by the user from its normal operating position, to each of several test positions, in which various items listed on a trouble shooting chart may be checked against the values actually indicated on the readout meter provided on that module. This leads to a determination by the user whether something is wrong with the module and it should be changed-out for salvage or repair, or if something is wrong off the module and in need of a part charge-out or a repair.

Abstract: A time multiplexed sensor monitoring system. A plurality of remote sensor units are connected to a central control unit by a two-wire bus line. Power is supplied to the remote unit sensors by the central control unit. Synchronization of the remote units is provided through momentary interruptions in the power supplied to the remote sensor units. The use of a single two-wire bus line for both application of DC signals to the respective remote sensor units and communication of data from the remote sensor units to the central control unit is facilitated by use of double tone multi-frequency (DTMF) signalling techniques.