What are the scaling requirements of a module?
A5. The scaling resistors Ra and Rb should be metal film types, 1% tolerance and have a temperature coefficient of 50ppm/°C or less to minimize drift. Note: you normally have to cut a link (on the module’s PCB) that is shorting out Ra. When scaling resistors have been fitted, it will be necessary to recalibrate the module. Please note that if potentiometers are used for scaling, their temperature coefficient will be greater than that of fixed value resistors. If measuring high voltages please remember that a standard leaded resistor typically has a maximum operating voltage of 250V (sometimes less). Scaling for above 200V should always be done externally to the meter. Metal oxide resistors often have a higher breakdown voltage than metal film, at a penalty of a higher temperature coefficient, (actual specifications should be carefully checked prior to use). Also bear in mind that scaling resistors should be of an adequate voltage rating for any transient, or fault conditions that may b
