This is the auto-generated ULOG format spec for the accel sensor message:
const char *__orb_sensor_accel_fields = "SENSOR_ACCEL:uint64_t integral_dt;uint64_t error_count;float x;float y;float z;float x_integral;float y_integral;float z_integral;float temperature;float range_m_s2;float scaling;uint32_t device_id;int16_t x_raw;int16_t y_raw;int16_t z_raw;int16_t temperature_raw;";
The multi-instance ID is in the header of the log message. It is not indicated by the msgID or the "name" of the message. Instead, the multi_id field in struct message_data_header_s specifies the instance number along with a bit labeled "active" in the FlightPlot code. This field was hardwired to 0x80 in logger.cpp, with comment "Non multi, active".