Signal measuring device

A signal measuring device measuring process signals in a signal measurement target section, the signal measurement target section including a plurality of detection units, each detection unit detecting a continuously varying process signal, the signal measuring device comprising:

• one input circuit for receiving the process signal from each detection unit;
• a signal switching unit for performing open/close switching between each detection unit and the input circuit;
• a signal processor connected to the input circuit and for processing the process signal;
• and
• a switching command circuit for outputting, to the signal switching unit, a switching command signal that corresponds to an open/close time set such that one of the detection units is connected to the input circuit, the switching command circuit for outputting, to the signal processor, a measurement command signal that corresponds to a stable measurement time which is set for each detection unit and after which the process signal inputted from the detection unit to the input circuit is stably measurable;
• wherein the signal measuring device comprises
• a constant current circuit coupled to the signal switching unit and configured to provide a detection unit, of the plurality of detection units, with a constant current via the signal switching unit,
• wherein:
• the signal switching unit includes a second input terminal, a second output terminal, a third input terminal, and a third output terminal, for the detection unit that needs a constant current,
• the detection unit that needs a constant current and the input circuit are connected via the second input terminal and the second output terminal,
• the detection unit that needs a constant current and the constant current circuit are connected via the third input terminal and the third output terminal, and
• the switching command circuit outputs the switching command signal to the second input terminal, the second output terminal, the third input terminal, and the third output terminal.