The movement consists of a bimetallic spiral which is expanded by the heat caused by the current circulating in it, driving the pointer. A second spiral, mounted in opposition, compensates the effect of the ambient temperature.
Due to its long response time, shor interval current peaks are not registered and the instrument indicates by a black pointer the mean of the r.m.s. current in a specified period of time (15 minutes). The maximum indication is registered by the position of the red pointer, dragged by the black one. By means of a sealable knob it is possible to resetthe red pointer to the position of the black one in order to make a new reading. The maximum demamd meters are used to monitor lias in feeders, transformers and electrical installations in general.
Overload capacity according to DIN 43780
Continuously 1,2 times nominal value
Short duration 10 times nominal value
Saturing current transformers shall be used to protect the instruments against overloads exceeding this rating.
Scales
The full -scale value is 1.2 times In, (In is the rated primary current of the current transformer). 90º scale, quadratic. Coarse-fine division.