1,197,370. Nuclear power plant. SIEMENS A.G. 11 Dec., 1968 [12 Dec., 1967; 15 Dec., 1967], No. 58989/68. Heading G6C. [Also in Division F4] In an installation including a once-through steam boiler the entire tube system of which extends right through a zone which is heated by a heat carrier which does not foul the heating surfaces, without interposition in that zone of headers or other mixing and separating vessels, signals representing the difference between the pressures at the inlet and outlet of the tube system and signals representing the rate of throughflow of the working medium, influence a load correction controller to bring the feedwater supply and the heating power into accordance with one another at least to the extent of avoiding thermal shock damaging the superheater when the boiler changes over to another working state. Parallel-connected boiler sections such as 3, 7, arranged around a nuclear reactor core 1, are heated by CO 2 circulated through the reactor core by fans 11. The pressure drop across the boiler tubes is measured by a differential pressure measuring device 26 or by separate devices at the boiler inlet and outlet, and the flow of feedwater is measured at, say, an orifice 29, the resultant signals being applied to a comparator 28 which compares them with signals from a storage device 25 representing predetermined desired values and supplies an output signal to a load correction controller 33 which influences the reactor control through a signal line 35 and/or influences the feedwater pump 18 or a feedwater regulating valve 19 through a feedwater controller 17. The pressure drop measurements provide a substitute for temperature measurements within the boiler which it is not feasible to make by reason of the inaccessibility of the boiler within the reactor envelope. To allow for an increase of the pressure drop occurring in the course of time, e.g. due to fouling or roughening of the inner surfaces of the boiler tubes, the final temperature at the steam outlet pipe 14 is measured at a point T and applied to the comparator 28 to provide an automatic correction, applied via a correcting unit 36, to the desired-value storage device 25. The correction may instead be made manually. If the steam outlet pressure is to be variable in dependence on load, signals representing the steam pressure P and the load L are applied to a computer 44 which yields a modifying signal applied, e.g., to the device 25. Devices 24, 38, 39 for monitoring the water level in the boiler tubes may also be used to perform the function of the device 26, i.e., to measure the pressure drop across the tubes. Each device 24, 38 or 39 operates over a different part of the total measurement range, and automatic change-over from one of these devices to another may be effected in dependence on load. 1,197,381. Measuring displacement. BENDIX CORP. 14 March, 1968 [20 March, 1967], No. 12526/68. Heading G4H. [Also in Division H3] In a displacement measuring system in which pulses representing the movement of a member are accumulated positively or negatively in a counter, a pulse generator 28 (Fig. 1) (see Division H3) is also connected to the counter, pulses being fed from the generator 28 to the counter to preset it to any predetermined value. In the embodiment described for measuring displacement in two directions, transducers 2, 2<SP>1</SP> receive signals from gratings 4, 4<SP>1</SP> as the member moves, these signals being shaped to give pulse trains on leads 20 or 22 and 20<SP>1</SP> or 22<SP>1</SP> connected to counters 24, 24<SP>1</SP>. A switch 32 selects which counter 24, 24<SP>1</SP> is connected to the pulse generator 28 for presetting and a push button switch 34 determines the direction of count, the frequency of the pulses depending on the setting of a multiposition switch 30.