Abstract: An interface circuit for use in a data transmission system has a first port for connection to a 16 wire data highway of the type proposed by the I.E.C. (International Electrochemical Commission) for the interconnection of instruments, and a second port capable of being connected to an eight-wire or two-wire data link. The interface circuit includes an encoding circuit operative to encode at least some commands applied to the first port, and an enabling circuit for selectively enabling data applied to the data terminals of the first port and the encoded commands to pass to the second port.

Abstract: A digital voltmeter for measuring an input voltage which can lie in any one of M successive ranges comprises an input scaling device which scales the input voltage to produce a voltage lying in a single predetermined range, and which also produces a range signal indicative of the range in which the input voltage lies. An analogue-to-digital conversion circuit then converts the scaled voltage to a corresponding digital signal which has up to N significant decade figures of resolution, where N<M. The voltmeter has a display unit with M decades, each of which represents a fixed order of magnitude of the input voltage, and control means responsive to the range signal to direct the digital signal to the group of N adjacent decades of the display means appropriate to the magnitude of the input voltage.

Abstract: Apparatus for measuring the phase difference between two electrical signals Asin (wt+.theta.), Bsin (wt+.phi.), given a reference signal Vsin wt generated by the apparatus, comprises a phase lock loop for generating a clock frequency f = 360F where F is the frequency of the reference signal. This clock frequency f is then used to tune a 360 stage CCD transversal filter which is used to filter successively the two first-mentioned signals, whose phase difference is then measured by a zero intercept system. The clock frequency f is used to give phase difference in degrees.The phase lock loop comprises a 90-stage CCD to which the reference signal is applied. The output of the CCD is applied to one input of a phase sensitive detector whose other input is connected to receive the reference signal, and the control signal produced by the phase sensitive detector controls a voltage controlled oscillator whose output is applied to the clock input of the CCD.

Abstract: In a spectrum analyzer, the analogue signal to be analyzed is periodically sampled and digitized, and the digit samples are formed into R successive arrays each containing 2N successive samples and each overlapping the previous array by 50%. The forward Fourier transforms of each array are then successively formed, and an array of 2P complex points is formed from the result of each transform, where L-P/2 and L+P/2-1 are the points which represent the upper and lower limits of a Vernier band to be studied in detail and each array extends from points L-P to L+P-1 (i.e. each array is twice the width of the Vernier band, and the Vernier band is symmetrically disposed therein): additionally, each array for which L and R are odd is complemented. The arrays thus formed are then each multiplied by a window function (effectively equivalent to a band pass filter), and the result is subjected to the inverse Fourier transform to form respective further arrays of 2P points.

Abstract: Digital calculating apparatus, which is particularly suitable for linearizing a digitized output signal produced by a non-linear transducer such as a thermocouple, comprises a store connected in a recirculating loop including combined adder and subtractor circuit, means for changing a number entered in the store to a predetermined target value by a linear or an exponential progression involving groups of N adding or subtracting-cycles, means for counting and storing the numbers of groups of cycles required to achieve the target value, and means for entering another number in the store and subjecting it to the same numbers of groups of M adding or substracting cycles, where M .ltoreq. N, to produce the required answer. For linearizing the digitized output signal x from a thermocouple, where x is given by T = a.sub.o + a.sub.1 x + a.sub.2 x.sup.2 + . . . ta.sub.n x.sup.