Abstract: A gas measuring device for measuring a presence of a target gas in a fluid medium includes a sensor having a sensing element and a heating element being configured to heat the sensing element to a predetermined operating temperature. The sensing element is responsive to the target gas such that at least one electrical property of the sensing element varies based on a presence of the target gas, and the electrical property of the sensing element is measured by the gas measuring device. The gas measuring device also includes a control circuit having a heating element controller connected to, and measuring an electrical property of, the heating element. The control circuit also includes a heater power supply supplying power to the heating element, wherein the heating element controller is connected to, and controls the operation of, the heater power supply based on the measurement of the electrical property of the heating element.

Abstract: A gas detector is provided. The gas detector includes a measurement source of optical radiation, a reference source of optical radiation, a measurement detector configured to provide an output signal indicative of a gas of interest, a reference detector configured to provide an output signal at least partially independent of the gas of interest, a measurement optical path extending from the measurement source to the reference and measurement detectors, and a sample region for receiving a gaseous sample. The sample region is located along the measurement optical path. A window is positioned in the measurement optical path downstream from the measurement source and upstream from the reference and measurement detectors. The window is partially transparent to optical radiation and partially reflective to optical radiation.

Abstract: A gas measuring device for measuring a presence of a target gas in a fluid medium includes a sensor case defining a sensor cavity extending from an open end of the sensor case, wherein the fluid medium flows into the sensor cavity through the open end. A sensor is positioned within the sensor cavity for sensing the presence of the target gas, wherein the sensor has a sensing element on one side of the sensor, and the sensing element is positioned within the sensor cavity such that the sensing element faces away from the open end.

Abstract: A gas measuring device for measuring a presence of a target gas in a fluid medium includes a sensor having a sensing element and a heating element being configured to heat the sensing element to a predetermined operating temperature. The sensing element is responsive to the target gas such that at least one electrical property of the sensing element varies based on a presence of the target gas, and the electrical property of the sensing element is measured by the gas measuring device. The gas measuring device also includes a control circuit having a heating element controller connected to, and measuring an electrical property of, the heating element. The control circuit also includes a heater power supply supplying power to the heating element, wherein the heating element controller is connected to, and controls the operation of, the heater power supply based on the measurement of the electrical property of the heating element.

Abstract: A gas detector is provided. The gas detector includes a measurement source of optical radiation, a reference source of optical radiation, a measurement detector configured to provide an output signal indicative of a gas of interest, a reference detector configured to provide an output signal at least partially independent of the gas of interest, a measurement optical path extending from the measurement source to the reference and measurement detectors, and a sample region for receiving a gaseous sample. The sample region is located along the measurement optical path. A window is positioned in the measurement optical path downstream from the measurement source and upstream from the reference and measurement detectors. The window is partially transparent to optical radiation and partially reflective to optical radiation.

Abstract: A system and method for measuring fluid flow rate in a system where fluid is pumped, such as a gas monitoring instrument where gas is pumped from a space such as a room or enclosure through a conduit to a sensor. The flow of gas through a pump is determined by measuring motor back-e.m.f. which is proportional to motor speed. In a system where motor speed is regulated by pulse width modulation of the motor drive voltage, the back-e.m.f. is sampled during intervals between the drive pulses applied to the motor, and in a further aspect the sampling is done at selected, spaced-apart or infrequent intervals such as once for every ten or once for every hundred motor drive pulses. Advantageously, in an instrument that uses a microprocessor and analog-to-digital converter to measure gas-concentration, the same microprocessor and converter can provide the PWM control of the pump, in response to the back-e.m.f. generated by the pump motor between the drive pulses.

Abstract: A system and method for measuring fluid flow rate in a system where fluid is pumped, such as a gas monitoring instrument where gas is pumped from a space such as a room or enclosure through a conduit to a sensor. The flow of gas through a pump is determined by measuring motor back-e.m.f. which is proportional to motor speed. In a system where motor speed is regulated by pulse width modulation of the motor drive voltage, the back-e.m.f. is sampled during intervals between the drive pulses applied to the motor, and in a further aspect the sampling is done at selected, spaced-apart or infrequent intervals such as once for every ten or once for every hundred motor drive pulses. Advantageously, in an instrument that uses a microprocessor and analog-to-digital converter to measure gas-concentration, the same microprocessor and converter can provide the PWM control of the pump, in response to the back-e.m.f. generated by the pump motor between the drive pulses.

Abstract: A gas detection sensor system including active and reference elements (Rsense, Rref) are arranged in a modified bridge circuit (12, 14, 22, 24) which allows power (Vbat) to be supplied seperately to the active and reference element (Rsense, Rref). A digal processor (30) monitors the resistances of the elements (Rsense, Rref) to control a pulse-width modulator supplying power to the elements, thereby maintaining nearly constant temperatures in the sensor elements (Rsense, Rref) and to translate the decrease in power needed to maintain constant temperature on the catalytic element into an output proportional to the concentration of combutible gas in air. The system periodically measures the resistance of the elements (Rref, Rsense) and enables dual operating modes of catalytic-bead detector. One active or reference element (Rsense, Rref) can alternately measure low concentrations of combustible gases up to the lower explosive limit (LEL) or measure high concentrations, up to 100% by volume.

Abstract: A gas detection sensor which combines the advantages of constant-temperature operation and PWM control for catalytic-bead, combustible-gas detectors. The active and reference elements of the gas detector are arranged in a modified bridge circuit which allows power to be supplied, using pulse-width modulation, separately to the active and reference elements. An advantage is that constant temperature can be maintained on the elements by using a relatively inexpensive digital processor to monitor the resistances of the elements to control the pulse-width modulator, and to translate the decrease in power needed to maintain constant temperature on the catalytic element into an output proportional to the concentration of combustible gas in air. Thus, a system embodying the foregoing periodically measures the resistance of one or more sensor elements (Rref and Rsense) and controls the electrical bias applied to the elements, using PWM, thereby maintaining nearly constant temperatures in the sensor elements.

Abstract: A system and method for measuring fluid flow rate in a system where fluid is pumped, such as a gas monitoring instrument where gas is pumped from a space such as a room or enclosure through a conduit to a sensor. The flow of gas through a pump is determined by measuring motor back-e.m.f. which is proportional to motor speed. In a system where motor speed is regulated by pulse width modulation of the motor drive voltage, the back-e.m.f. is sampled during intervals between the drive pulses applied to the motor, and in a further aspect the sampling is done at selected, spaced-apart or infrequent intervals such as once for every ten or once for every hundred motor drive pulses. Advantageously, in an instrument that uses a microprocessor and analog-to-digital converter to measure gas-concentration, the same microprocessor and converter can provide the PWM control of the pump, in response to the back-e.m.f. generated by the pump motor between the drive pulses.

Abstract: A cursor generator for an oscilloscope presents a cursor line or lines in juxtaposition with waveforms on an oscilloscope display, wherein the cursor is formed of a plurality of discrete points or dots. The deflection signal for generating the cursor is preferably supplied from the oscilloscope's character generator, while the analog positioning voltages for the cursor are also used in sweep delay comparison portion of the oscilloscope for initiating the oscilloscope's delayed sweep.

Abstract: A method for digitally measuring waveforms is provided in which absolute and relative amplitudes and time information of electrical signals is electronically determined. A pair of cursors, which are operable in both independent and tracking modes, are used to provide alignment with reference points and selected measurement points so that the voltage difference between the cursors may be utilized by a digital voltmeter to provide the measurement data.

Abstract: In accordance with the present invention, a control circuit for operating a delayed sweep oscilloscope includes a reversible counter which may be selectively incremented or decremented to establish a number of trigger-circuit operating functions and modes, such as trigger source selection, coupling, level, and sweep mode. A plurality of light sources behind a plastic overlay laminated to the front panel indicate the various functions and modes.

Abstract: An apparatus and method are provided for automatically calibrating sweep waveforms produced by a sweep generating circuit in response to digital time reference words produced by a system controller. Time interval measurements are made directly on sweep waveforms and sweep slope values are derived therefrom. The sweep slope values are used by the system controller to adjust the digital time reference words.

Abstract: An oscilloscope vertical calibration system is provided in which gain control elements in one or more vertical input channels are automatically controlled with respect to cursor voltages applied to the vertical output amplifier. Such calibration process is performed for each deflection factor setting either manually or automatically and the correct gain control signals are stored in memory.