Saelig Company now offers the NanoRanger NR-01 – designed by AltoNovus – an affordable, highly accurate 3.5-digit DC ammeter created for accurately measuring very low currents. With automatic dynamic ranging (nine ranges across 8.5 decades), The device measures currents from 1nA up to 800mA with a maximum resolution of 10pA. Each instrument is provided factory calibrated, removing the need for high-cost precision components in the design, and therefore, keeping the purchase price low. The current is measured with a 12-bit ADC, which is oversampled and automatically averaged to provide a 16-bit result. Samples are taken every 170uS. Readings are shown every 300mS, built up from 180 averaged samples to remove line noise (both 50Hz and 60Hz). An alternative ‘Fast Sample’ mode can sample at 150 measurements per second.
The backlit 11-digit 128 x 64 LCD offers a wealth of information for current readings; for instance, mA, uA, nA, and pA are all on one line. A Running Average reading (current and time elapsed) enables the user to measure the power consumption of events, such as radio transmissions. The Range Coverage Bar displays the ranges covered throughout the measurement; it can be ‘bracketed’ or limited to only one range. A signal-to-noise ratio display displays how much noise, or AC, is present on the current signal. Minimum and maximum ranges can be altered to limit the auto-ranging or fixed at a single range.
Challenges occur when attempting to measure the power consumption of low power circuits operating in offline or standby mode. Typically, current consumption falls into the nA or pA ranges that are beyond the ability of most DMMs, but this device measures accurately into these ranges. A 6.5-digit DMM with 1nA resolution may only have a lowest range of 2.000000mA, and the absolute accuracy may only be +/-500nA. The device has selectable ranges for each decade of measurement. It is designed with a fully isolated USB interface for device control and data export. Being completely isolated means that a USB connection will not adversely affect the measurements.
The device has been created specifically to reduce burden voltage to lower than 50mV when taking low power current measurements. A large burden voltage may affect the circuit being measured, corrupting the measurement. For this reason, it is desirable for burden voltage to be maintained as low as possible.