True-rms AC ammeters from Murata interface directly with current transformers

True-rms responding ammeters provide accurate and reliable performance in switching power supply applications where input currents are typically distorted and do not resemble the universally recognised sine-wave shape. Other approaches to measurement such as average responding AC ammeters can result in reading errors in excess of 20% of their full-scale output. In critical applications, this may lead to inadvertent overloading of circuit breakers or fuses, which in turn can cause costly power outages.

The ACA5-20RM family scales and displays the output of 5A ‘donut’ style current transformers (CTs). The series covers three ranges: 100A, 200A and 500A. A choice of 85 to 140VAC or 170 to 264VAC (at 47 to 63Hz) operating supply voltages is offered for each range. Maximum power consumption is less than 50mA and operating temperature range is 0ºC to +60ºC.

Crest factors (the ratio of peak current to rms current) for the ACA5-20RM series are as high as five and all models specify 2000V isolation between the AC power source and the external 5A CT. The functionally complete design uses a reliable single-board construction, has a built-in low-burden toroid sensor and a bright red LED display with 9.4mm (0.37in.) high characters. Where specific applications require, Murata Power Solutions can supply 100:5, 200:5 and 500:5 accessory CTs.