A method and apparatus are provided wherein there is associated with each value of a measurement of a parameter such as pressure, for transmission through an electromagnetic coupling device, a time duration or period which is a function of the measured value. A first, start signal of relatively short duration is transmitted and thereafter, at the end of a period which is a function of the parameter, a second, ending signal of relatively short duration is transmitted. A receiving device which is responsive to said signals, measures the elapsed time between them, i.e., measures the length of the intervening period, and converts this measurement into a measure of the parameter.