ABSTRACT
All measuring instruments have an indicator to show measured data. Some instruments will instead, or in addition, send pulses as an output signal. This method is common when measuring an amount such as tons or cubic metres. Inside almost all measuring instruments, there are several signal converters and calculators. For measuring an analogue signal correctly, some fundamental electrical knowledge is needed. Common problems in mA-signal circuits are faults in the ground (or earth) connection, especially if more than one receiving instruments are connected in series. Some devices have no galvanic separation between signal zero (reference) and supply zero (reference), and this can result in problems. One of the main purposes for industrial measuring instruments is to control a process. Linearisation is required when a sensor produces a non-perfect signal. Process design drawings are very useful, both when designing new systems and when searching for problems. Various standards are available for this, detailing how symbols should be used for various components.
