4.25. Interlock
4.25.2. Description
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graph interlock_schematic {
subgraph cluster_main {
label="main interlock circuit";
node [shape=rectangle,group=1]
nd_static_supply
nd_interlock_high
nd_interlock_low
nd_low_side_regulation
nd_system_ground;
node [shape=plain,group=1]
nd_low_side_cs
nd_low_side_threshold_cs;
nd_static_supply [label="static low-power supply"];
nd_interlock_high [label="interlock connector high"];
nd_interlock_low [label="interlock connector low"];
nd_low_side_cs [label="low-side current sense (100mA = 4V)"];
nd_low_side_regulation [label="low-side current regulation (to 50mA)"];
nd_low_side_threshold_cs [label="low-side current threshold (low = current above 10mA)"];
nd_system_ground [label="system ground"];
edge[color=blue]
nd_static_supply -- nd_interlock_high [style=bold];
nd_interlock_high -- nd_interlock_low [style="bold,dashed",label="external connection"];
nd_interlock_low -- nd_low_side_cs [style=bold];
nd_low_side_cs -- nd_low_side_regulation [style=bold];
nd_low_side_regulation -- nd_low_side_threshold_cs [style=bold];
nd_low_side_threshold_cs -- nd_system_ground [style=bold];
}
node [shape=rectangle,group=2]
nd_diagnostic_supply;
node [shape=rectangle,group=3]
nd_high_side_vs
nd_low_side_vs;
node [shape=plain,group=2]
nd_high_side_cs;
nd_diagnostic_supply [label="diagnostic high-power supply"];
nd_high_side_cs [label="high-side current sense (133mA range)"];
nd_high_side_vs [label="high-side voltage sense (resistor divider 3k9/(5k6+3k9))"];
nd_low_side_vs [label="low-side voltage sense (resistor divider 3k9/(5k6+3k9))"];
edge [color=orange]
nd_diagnostic_supply -- nd_high_side_cs;
nd_high_side_cs -- nd_interlock_high;
nd_interlock_high -- nd_high_side_vs;
nd_interlock_low -- nd_low_side_vs;
}](../../../../_images/graphviz-98b9e099b53f4dcdc261210800c1e94492a78b2a.png)
Fig. 4.10 Simplified schematic of the interlock circuit
The purpose of the interlock circuit is that the embedded software can recognize that an external safety circuit has been opened. This is achieved through a monitor current that is supplied to an external connector. The application expects that the rest of the safety system closes this path when it is working as expected. Typically, this is used with emergency stop switches or similar devices. A simplified schematic of the interlock circuit is shown in Fig. 4.10.
4.25.2.1. Circuit description
The interlock circuit consists of a main path that is continuously supplied by
the static power supply of the foxBMS Master Unit.
In Fig. 4.10 this is called
static low-power supply.
This supply does not have to be enabled and is powered by the 5V rail of the
peripheral supply.
The interlock is closed through the connector that makes the external
connection of interlock connector high with interlock connector low.
As a diagnostic measure, the low-side current sense allows to monitor the
current on the low-side of the interlock connector.
The monitoring circuit scales 0mA to 100mA from 0V to 4V with a linear relation.
For the case that additional diagnostic features are enabled, the
low-side current regulation limits the low-side current to 50mA.
As a last point in the measurement chain, a low-side current threshold
comparator circuit, pulls a pin low in the case that the threshold of 10mA
interlock current is surpassed.
This is the main detection method of detecting a closed interlock.
Additional diagnostic features consist of the voltage measurements of the high and low pins of the external interlock connector. Moreover, dedicated current measurements at the low- and high-side of the interlock connector increase the diagnostic possibilities.
The high-side voltage sense and the low-side voltage sense allow the
measurement of the voltages of the respective interlock connector pins.
Together with the low-side current sense circuit this allows an estimation of
the resistance of the external part of the interlock.
All voltages are measured using a resistor divider consisting of a 5k6 ohm and
a 3k9 ohm resistor.
An additional switchable power supply imprints a higher current on the
interlock path to increase the robustness of the interlock. This current can
be measured using the high-side current sense measurement.
The measurements of voltage and current on both high-side and low-side can be used for checking the plausibility of measured values.
4.25.2.2. Software description
The interlock state is read via a feedback input pin. If this pin is low, then the interlock is closed. If the pin is high, the interlock is open.
The feedback is checked in the interlock state machine. It reports an error
via the DIAG module if the interlock is open.
The interlock feedback can be deactivated via the define
BS_IGNORE_INTERLOCK_FEEDBACK. If set to true, the feedback function
will always return ILCK_SWITCH_ON.
In addition to the feedback pins, the ADC inputs of the MCU also monitor the voltages and currents described in the section Circuit description. Currently, these readings are only stored in the database (Section 4.7). They can be used for further diagnostics.
