Abstract: Electrical signals representing analog values of variables to be measured are sampled and multiplexed onto a common conductor. When the analog values are generated by transducers having a logarithmic characteristic, the signals are linearized by a log amplifier prior to being multiplexed. The ranges of the analog signals are made similar to facilitate use of a common display. A single analog-to-digital converter generates digital outputs representing the amplitudes of the respective analog samples and the digital outputs control display logic for operating the common display. A sequence timer controls operation of the multiplexer, analog-to-digital converter, display logic, and the display itself. Facility for manual override to display selectively any of the variables is provided, as well as an alarm indicator for generating an audible or visual alarm signal in the event any variable exceeds (or drops below) a predetermined reference level.

Abstract: A capacitor of limited storage capacity is charged and discharged under control of a switching arrangement. The switching arrangement functions to connect the capacitor to a first steady current source of one polarity for a fixed first interval in each cycle of an input signal, and connects a second steady current source of opposite polarity to the capacitor for the remainder of the input signal cycle so that the voltage stored by the capacitor changes polarity when the frequency of the input signal traverses a threshold value. By shunting the capacitor with a fixed resistor, an output voltage linearly dependent on the input frequency can be obtained. By connecting the switching arrangement to connect the first current source to the capacitor for a fixed interval of time in each cycle of a first input signal, and to connect the second current source to the capacitor for a fixed interval of time in each cycle of a second input signal, a difference frequency discriminator function can be provided.