5. IMD Testing

The Insulation Measurement Device measures the insulation resistance between the high voltage potentials. Low insulation resistance induces a high safety risk, to sense this danger the IMD is used. To ensure the correct functionality testing the IMD on the actually implemented system is very important.

simplified diagram of imd — Fig. 5.8 Resistance measured by the IMD (in red)

5.1. Test preparation

Needed to test the IMD are:

foxBMS 2 workspace as described in Getting Started with foxBMS 2
resistors with different values are required

Table 5.58 important resistance values
R_max *	R_warning	V_critical
50\({M\Omega}\)	750\({k\Omega}\)	500\({k\Omega}\)

* maximum resistance measurable by the supported IMD devices (see Insulation Measurement Device).

5.2. Testing resistance

First data_blockInsulationMonitoring and data_blockErrors is added to the watch window of the debugger to observe the output of the IMD.

To test if resistance is read correctly put a resistor between the high voltage connectors and the ground/chassis potential.

After a slight delay it reports the resistance of the resistor which can be read in the insulation monitoring data table.

If the resistance is lower than the warning threshold of 750\({k\Omega}\) the warnableLowInsulationResistanceError will be set. If the resistance is lower than the critical threshold of 500\({k\Omega}\) the criticalLowInsulationResistanceError will be set.