Measurement Procedure
CANBench TrueZ v1.1 — Fabricated prototype, sole built unit. V1.1 is electrically identical to the V1.2 schematic refresh but predates the InvenTree symbol-library migration; the schematic component metadata reflects legacy SCADYS naming. Testing and bench validation reference this V1.1 hardware.
Other versions: v1.2 — schematic refresh (next version)
Workflow for resolving a DUT's conducted-emissions signature into its common-mode and differential-mode components. Assumes the bench is cabled per Quick Start and the analyser is configured per Spectrum-Analyser Setup.
1. Validate the analyser noise floor
Terminate the analyser input directly with 50 Ω (no TrueZ connected) and sweep the band. This is your reference floor for the session — the same step as for the CANBench Duo. A higher-than-usual floor means a bad cable, a contaminated terminator, or local interference; fix it before proceeding.
2. Baseline (Duo powered, DUT disconnected)
With the TrueZ cabled to the Duo's two LISN outputs and the analyser on the CM-25Ω output (50 Ω terminator on DM-100Ω), apply Duo supply power with the DUT disconnected. Sweep. Peaks here come from the bench supply or the environment, not the DUT — record them as the environmental baseline.
3. Common-mode sweep
Connect the DUT and power it normally. With the analyser on CM-25Ω (J4) and a 50 Ω terminator on DM-100Ω (J5), sweep. This is the common-mode conducted-emissions signature — disturbance the DUT couples to both supply lines together (typically via parasitic capacitance to chassis/ground).
4. Differential-mode sweep
Move the analyser to DM-100Ω (J5) and put the 50 Ω terminator on CM-25Ω (J4). Sweep. This is the differential-mode signature — disturbance that returns line-to-line through the supply rather than via chassis coupling.
5. Apply the low-end correction
Below ≈ 0.5 MHz the transformers droop, so the bottom of the band reads low. Apply the TrueZ correction curve (post-processing) to the CM and DM traces before comparing absolute low-band levels. The curve is currently a first-order simulated model, pending the golden-prototype measurement that will replace it (see Tasks) — treat low-band absolute levels as provisional. Above ~1 MHz no correction is needed for relative work.
6. Interpret
Compare the CM and DM traces against the baseline and against each other. Which mode dominates tells you which mitigation to reach for — see Interpreting Results.
Two results invalidate the measurement: mismatched input cables (converts DM↔CM) and a non-50 Ω analyser input (breaks the CM-25Ω / DM-100Ω calibration). Confirm both before trusting a trace — see Common Pitfalls.