GB1449069A - Heating controller - Google Patents

Abstract

1449069 Automatic temperature control ADOLPH SAURER Ltd 23 Sept 1974 [21 Sept 1973] 41370/74 Heading G3R A control system for use with an interior heating installation has means for changing both the slope and the position of a controller characteristic (as explained below) together with means for determining which of these two adjustments is appropriate. In Fig. 1, curve a shows the relationship, for a given installation, between external temperature tA and heating medium (or heating surface) temperature THV to attain required internal temperature conditions. The controller characteristic is the relation between tA and t HV determined by the control system and this is a straight line such as a<SP>1</SP> which approximates to the curve a. The specification shows that at high external temperatures the divergence between a and a<SP>1</SP> is best corrected by a bodily shift of a<SP>1</SP> but that at low temperatures it is better to vary the slope of a<SP>1</SP>. The control circuit of Fig. 5 uses a known bridge configuration Fig. 4 (not shown) improved by the provision of means 5 to indicate whether the external temperature is high or low. Figs. 6 and 7 (not shown) depict variants of the Fig. 5 circuit. In Fig. 5, the resistance of elements 3 and 4 vary with the external and the heating medium temperature respectively and the output between points 41, 44 leads to an amplifier which controls the heating means. This causes t HV to rise as tA falls in accordance with a line such as a<SP>1</SP> in Fig. 1, the slope of which depends on the settings of potentiometers 2a, 2b and the position of which depends on the setting of potentiometer 1. The output between points 43 and 45 depends on the potential of point 42 and hence on the external temperature. A threshold switch 5 responds to this output by means of a signal which informs an operator that any necessary adjustment should either be a 'positional' adjustment using potentiometer 1 or a 'slope' adjustment using potentiometer 2b. Alternatively, the potentiometers 1 and 2b may have a common operating knob and the output from switch 5 may control the coupling of this knob to the appropriate one of the two potentiometers.