AC voltage/current standard for calibrating measuring instruments

The Yokogawa 2558A is a new precision AC voltage/current standard that offers a simple stand-alone solution for the calibration of measuring instruments and power sensing devices including power meters, clamp meters and current transformers.

The 2558A offers exceptionally high accuracy - 0.04% on AC voltage and 0.05% on AC current - and a choice of wide output ranges from 1.00 mV to 1200.0 V AC and 1.00 mA to 60.00 A AC (expandable to 120 A by using two units in parallel).

Operation is intuitive, with front-panel rotary dials and switches for each function and each digit of the 4½-digit display. A sweep function, output divider and internal phase shifter are incorporated, and a range of computer interfaces enables the 2558A to be incorporated in an automatic test system in a production environment.

The instrument operates over a wide frequency range from 40 to 1000 Hz with a frequency accuracy of: ±50 ppm, including the provision of fixed frequencies of 50/60 Hz (commercial) and 400 Hz (marine and aviation). The high frequency accuracy also enables it to be used to calibrate frequency meters.

Multiple 2558As can be synchronised using the internal phase shifter, allowing two instruments to be used as accurate sources of voltage and current for calibrating power meters. An output divider enables linearity tests to be carried out efficiently.

Dials and switches are provided for each digit and function, and traditional 7-segment LEDs provide clear visibility. When the deviation dials are adjusted to check the full scale value on the meter, the deviation from the main output setting is displayed as a percentage of full scale.

With the sweep function, the output (voltage, current or frequency) can be swept from 0% to 120% of the main set value with sweep times of 16, 32 or 64 seconds. This function is particularly useful for carrying out "sticking" tests on analogue meters and indicating instruments. Using the internal phase shifter, a complete power calibration system can be assembled using two 2558A units and one power meter.

Typical users include calibration laboratories as well as suppliers of panel meters, indicating instruments, analogue testers, clamp meters, protection relays and current and power transducers.

The Yokogawa 2558A is a compact bench unit measuring 132 high × 426 mm wide × 400 mm deep and weighing approximately 20 kg.