Voltcraft cc 421 calibrator voltcraft cc 421 p the voltcraft cc 421 current calibrator is a high precision calibration tool for your measurement device the current source can supply up to 24ma max at 400ohm dc current measurement up to 24madc and loop current measurements the cc 421 connects four functions in one device precise dc source measurement of process currents supplying and measuring 2 conductor loop current systems and precise dc source it is simple to use with only 3 slid