# Typical Behavior This section contains information regarding typical Joulescope behavior. ## Step Response Joulescope is a shunt ammeter with incredibly fast autoranging. This section contains typical autoranging measurements. The test setup includes a Joulescope, a custom load board, a power supply, a computer, and some cables. A custom load board is the Joulescope target. The load board was specifically designed for the sole purpose of creating very fast, repeatable edges. It has a 1 MΩ resistor in parallel with a 1Ω resistor. The board contains a momentary pushbutton and debouncer, which is the input to the MCP1416 MOSFET driver. The MCP1416 drives the FDMC7678 MOSFET, which enables or disables the 1Ω resistor. The entire circuit is powered by a 9V battery and connected to the Joulescope OUT. The power supply is a Siglent SPD3303X-E bench supply configured for 1.00V and 2.9A. The supply is connected to Joulescope IN. Any bench supply with reasonable transient performance should do.  The step response test setup The normal Joulescope user interface software captures data while pressing the target board’s switch to toggle the MOSFET & 1Ω resistor. A custom Python script reads the data, processes the data, and creates plots. The python script finds each edge and aligns them so that they can be plotted together. The plots show rising edges in the left column and falling edges in the right column. The first capture “step_2A.png” is the baseline with Joulescope auto-ranging disabled and set to a fixed 2A range. The rise time you see is due to the Joulescope bandwidth. The actual edge is much, much faster.  Step response with fixed 2A range The second capture “step_autorange.png” is with auto-ranging. The two samples after over-range tend to contain “garbage” data that messes up the y-axis range, so they are omitted. These samples are captured at 2 MSPS (500 ns). Joulescope’s stated bandwidth is 250 kHz (4 µs = 8 samples).  Step response with autoranging The Joulescope specification states that range switching occurs within 1.2 µs max. This specification determines how much (or in the case of Joulescope, how little) voltage drop happens when the target changes current demands. The Joulescope specification gives over-range settling time is 2 µs typical with 5 µs max. This specification determines how well Joulescope can measure data through the transition. Any auto-ranging ammeter needs to be VERY fast to limit voltage variations at the target device, and Joulescope was designed to meet these demanding requirements.