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About Testing
This page explains the engineering context behind each test available in open-EE-workbench — what it measures, why you'd run it, and what the results tell you.
For configuration details and parameter references, see the linked pages.
Tab: Automation → DC Sweep
→ GUI - Automation
A DC sweep steps a PSU through a voltage or current range and records measurements at each point. It is the most general-purpose test in the toolkit.
Why: Any circuit element or system with a V-I relationship can be characterised with a DC sweep. The result is a curve (or a family of curves in nested mode) that describes how the circuit behaves across its operating range.
Common uses:
- Load regulation — sweep load current while measuring output voltage to characterise a PSU or regulator's output impedance
- Efficiency mapping — sweep input voltage and/or load current while measuring input and output power
- Component characterisation — sweep voltage across a diode, resistor, or passive component while measuring current
- Bias point validation — verify a designed operating point is where the circuit actually sits
Sweep modes:
- Single — one variable swept, straightforward curve
- Simultaneous — all configured channels step together; useful when two supplies must track each other
- Nested — outer channel(s) step slowly while the inner channel sweeps fully at each step; produces a 2D data grid equivalent to a family of curves. This is the mode used for transistor output characteristics and efficiency maps.
Tab: Automation → PSU Interrupt
→ GUI - Automation
The supply voltage is held at V1, switched off or to a different level (V2) for a defined interrupt duration, then restored to V3. A scope captures the voltage and current waveform during the transient.
Why: Real circuits are not powered by ideal sources. Momentary dropouts, brownouts, power sequencing, and hot-plug events all cause transients that can reveal design weaknesses invisible under steady-state testing.
Common uses:
- Bulk capacitance measurement — the discharge slope during a dropout directly gives C = I·dt/dV
- Hold-up time validation — verify a circuit survives a dropout for its required duration (e.g. 20 ms for IEC 61000-4-11)
- Power sequencing — check that rail-sequencing constraints are met across a multi-rail system
- Load transient response — measure how quickly a regulator recovers when load current steps
- Brownout behaviour — confirm that an MCU or system resets cleanly below its undervoltage lockout threshold
Tab: Automation → AC Sweep
→ GUI - Automation
An AWG steps through a list of frequencies while a scope or DMM measures the output amplitude at each step. The result is an amplitude-vs-frequency table — a Bode magnitude plot.
Why: The frequency response of a circuit is one of its most fundamental characteristics. Almost every analogue system has a bandwidth, a roll-off, or a resonance that matters for its intended application.
Common uses:
- Filter characterisation — measure -3 dB corner frequency, roll-off slope, and stopband attenuation
- Amplifier bandwidth — find the -3 dB bandwidth and confirm gain flatness across the passband
- Resonant circuits — locate the resonant frequency and measure Q factor of LC networks or piezo devices
- Feedback loop gain — break the loop and sweep to measure gain margin (combining with phase measurement from a more capable instrument)
- Cable / connector / PCB trace characterisation — identify frequency-dependent losses
Tab: Automation → DMM Logger
→ GUI - Automation
Continuously reads one measurement (voltage, current, resistance, or temperature via an appropriate probe) from a DMM and logs it with a timestamp.
Why: Many real-world effects only show up over time: thermal drift, ageing, settling transients, environmental sensitivity. A logger turns a DMM into a data recorder.
Common uses:
- Thermal coefficient measurement — log a resistor, reference, or oscillator while a temperature chamber ramps; extract TC from the slope
- Settling time — measure how long a reference, ADC input, or filter output takes to reach a stable value after power-up or input change
- Long-term stability / ageing — record a voltage reference or clock frequency over hours or days
- Environmental monitoring — log temperature, humidity (via appropriate sensor), or supply voltage during a thermal soak or vibration test
Tab: Automation → Waveform Analysis
→ GUI - Automation
Applies a waveform from an AWG, autoscales the scope, and automatically measures frequency, Vpp, rise time, fall time, and overshoot. Saves a screenshot and a CSV of results.
Why: Signal integrity and timing parameters are often checked repetitively — incoming inspection, production test, or regression testing after a design change. Automating the scope setup and measurement sequence removes human variability and saves time.
Common uses:
- Signal integrity check — quickly verify rise/fall times and overshoot on a digital signal at the board output
- Clock accuracy — measure frequency against a nominal value
- Driver characterisation — compare output waveform shape across voltage, temperature, or load conditions
- Pass/fail screening — record waveform parameters across a batch of boards to catch outliers
The tests below live in the Plot Specific tab rather than the Automation tab because each one produces a specific, well-defined plot with a canonical shape — the kind of curve you would find in a component datasheet. The axis meanings are fixed, the output is rendered as a live canvas during the sweep, and the result can be read directly without post-processing.
The Automation tab covers generic parametric tests where the output columns and chart are user-configurable. Plot Specific covers tests where the measurement itself defines what the plot should look like.
Tab: Plot Specific → Static Characteristic
→ GUI - Plot Specific
Sweeps the collector-emitter (V_CE) or drain-source (V_DS) voltage while holding base current or gate voltage at a series of fixed levels. Produces a family of I_C / I_D curves on a single canvas — the transistor's output characteristic.
Why: The output characteristic is the foundational datasheet plot for any transistor. It describes how the device behaves as a controlled current source, where its saturation region begins, and what its output resistance is. Running this measurement on an actual device reveals how it compares to datasheet typical curves and whether a particular sample is within spec.
What the curves tell you:
- h_FE / β (BJT) — the ratio of collector current to base current at any operating point; read directly from the spacing between curves
- Early voltage (BJT) — extrapolate the quasi-linear slope of the curves in the active region back to the V_CE axis; the intersection is −V_A, a measure of output resistance
- Output resistance r_o — the slope of I_C vs V_CE in the active region; flatter curves = higher r_o = better current source behaviour
- Saturation voltage V_CE(sat) — the knee of each curve; important for efficiency in switching circuits
- Safe operating area (SOA) — the envelope of all curves defines the region where the device can be operated without damage
BJT CC mode note: Base current steps in constant-current (CC) mode give cleanly spaced curves regardless of V_BE variation with temperature. This is how the datasheet characteristic is typically measured.
Tab: Plot Specific → Transfer Characteristic
→ GUI - Plot Specific
Holds the collector/drain at a fixed bias voltage and sweeps the base-emitter (V_BE) or gate-source (V_GS) voltage. Plots I_C / I_D vs gate/base voltage — the transistor's transconductance curve.
Why: The transfer characteristic describes how the input voltage controls the output current. It is the primary measurement for extracting transconductance (gm) and, for FETs, threshold voltage (V_th). These parameters directly govern small-signal gain and the bias point required for a given quiescent current.
What the curve tells you:
- Threshold voltage V_th (FET) — the gate voltage at which drain current starts to flow; extrapolate the linear region of the √I_D vs V_GS curve to the x-axis
- Transconductance gm — the slope dI_D/dV_GS (or dI_C/dV_BE); higher gm = more gain per unit bias current
- Turn-on characteristic (BJT) — the exponential I_C vs V_BE curve; its slope in log scale gives the ideality factor; the 60 mV/decade room-temperature slope is a useful sanity check
- Bias point design — read the gate/base voltage required to set a target quiescent current directly from the curve for the actual device under test, rather than relying on datasheet typical values
Tab: Sandbox
→ GUI - Sandbox
A general-purpose parametric test builder. You define the loops (what to sweep and how) and the actions (what to measure at each step). Any combination of instruments can be used.
Why: The built-in tests cover common measurement patterns, but engineering work constantly throws up variations — three nested loops instead of two, a settle-until-stable step before each measurement, logging three quantities simultaneously, or a sequence that doesn't fit any standard template. The Sandbox exists for everything else.
Where it fits: If a test you build in the Sandbox keeps proving useful and produces a well-defined, recognisable plot, it is a good candidate for promotion to the Plot Specific tab as a first-class test with its own card and live canvas.
Examples of what can be built:
- A 3D efficiency map sweeping both input voltage and output load current
- A thermal characterisation that waits for a set temperature before each I-V curve
- A battery discharge profile logging voltage, current, and temperature simultaneously over time
- An arbitrary stimulus-response test combining AWG, PSU, scope, and DMM in a single automated sequence