Each of the sixteen Analog Sensor channels is implemented as a software-controlled tension divider with 12 bits resolution (see functional diagram below). The 12-bit normalized value specified from the user interface, is transferred via the FPGA to the digital-to-analog converter of the channel, which produces an output signal (OUT_Ax) referenced to the low and high value of the external reference voltage supplied via the ELCO-56 connector.
Each channel can drive up to 200 mA within the voltage operating range and include a thermal protection circuit.
Reference voltage selection
The card allows supplying the individual reference voltage range for each channel via the REF_Lx/Hx pins of the ELCO-56 connector.
In addition, on Rev 2 of the card, two input pins (COM_REF_L/H) allow supplying a common reference. In the ASM Configuration Panel, the user can specify which reference, individual or common, is used for each channel.
The ASM thus does not use the rail input voltage provided by the power backplane, unless the GND and BATT pins are routed externally to the reference pins of the module.
Channels 12, 13, 14 and 15 can also be configured to have a linear, instead of ratiometric, output with respect to their references.
The activation of this feature is controlled via the ASM Configuration Panel of each ASM module. When it is enabled, an ax+b scaling is applied over the [ 0:1 ] value specified in the run-time panel. It is thus recommended to set the value to 1 in the panel when using this mode.
Different gain and offset values can be specified for each of the four channels. The individual gain and offset values are not accessible via the User interface but can be changed via the RT-LAB interface, or via a python script if an alias is set to these controls.
For example, for channel 12, the path to the gain and offset control blocks in the model are :
- offset : td/SM_Controller/Subsystem Modules/Subsystem AnalogSensorsModule 0/Subsystem OUT_A12, 13/Constant Offset OUT_A12/Value
- gain : td/SM_Controller/Subsystem Modules/Subsystem AnalogSensorsModule 0/Subsystem OUT_A12, 13/Gain OUT_A12/Gain