The automotive OEM specs do not specify how to configure the DUT during CISPR 25 chamber ambient measurements. DUT must be unpowered, all other DUT support equipment must be powered and as much as possible functional to correctly evaluate RF emissions noise floor before start testing. This leaves at least three scenarios for how to configure the DUT.
1) Disconnect the DUT from test harness.
- Test harness connectors are removed from
- DUT is unpowered.
- The 1.7 m test harness is unterminated on DUT side, no potential ground loops with Load Simulator.
- The 5uH LISN remains present.
- The Load Simulator and all support equipment remains powered.
2) Disconnect DUT's B+ line from LISN output.
- Test harness connectors are plugged into DUT.
- DUT is unpowered by disconnecting B+ line LISN input from Battery.
- The 1.7 m test harness terminated on both ends, therefore potential ground loops with Load Simulator are possible.
- The 5uH LISN remains present.
- The Load Simulator and all support equipment remains powered.
3) Diconnect DUT's B+ line from LISN output.
- Test harness connectors are plugged into DUT.
- DUT is unpowered by disconnecting DUT B+ line from LISN output.
- The 1.7 m test harness terminated on both ends, therefore potential ground loops with Load Simulator are possible.
- The 5uH LISN is not present anymore, and this somehow violates CISPR 25 requirement.
- The Load Simulator and all support equipment remains powered.
Christian Rosu