ADC – Analog data acquisition

The ADC block is used to retrieve the measurements from an analog input of the B-Box or B-Board.

This help documentation deals with the software part of the analog data acquisition. To set-up the hardware part, please refer to the following documents:

• Analog front-end configuration on B-Box RCP (PN105)
• B-Box RCP datasheet (PDF)
• B-Board PRO datasheet (PDF)

Simulink block

Signal specification

• The output signal returns a single-precision floating-point value representing the measured quantity in its physical unit (e.g. Volts, Amperes). When use ADC history is selected, it returns a vector of the N last values, as documented in Oversampling (PN154).
• The sim input signal is used in simulation and documented in Simulation essentials with Simulink (PN135).
• The > input signal needs to be connected to the CONFIG block in order to account for the exact sampling instant in simulation.

Standard parameters

• Device ID selects which B-Box/B-Board to address when used in a multi-device configuration.
• Input channel selects which physical input channel to read from (e.g. 0 to 15 on B-Box RCP).
• Quick configuration loads the parameters of an imperix sensor.
• Sensor sensitivity is the sensor sensitivity in Volts per measured unit (e.g. V/V for a voltage sensor and V/A for a current sensor).
• Sensor output offset compensates for the sensor offset. It is expressed in Volts at the output of the sensor.
• Programmable gain value must match the configuration set on the frontpanel of the B-Box.
• Match B-Board input full-scale must be checked if the device is a B-Board PRO. It forces the programmable analog gain to x2, to account for the +/- 5V input full-scale of the B-Board PRO (as opposed to +/- 10V on the B-Box RCP).

Advanced parameters

• Use ADC history enables the possibility the retrieve the N last sampled values.
• History depth (samples) is the number N of values to retrieve.

PLECS block

Signal specification

• The output signal returns a single-precision floating-point value representing the measured quantity in its physical unit (e.g. Volts, Amperes). When ADC history is enabled, it returns a vector of the N last values, as documented in Oversampling (PN154).
• The target inport (only visible at the atomic subsystem level) is used in simulation and documented in Simulation essentials with PLECS (PN137).
• The > input signal needs to be connected to the CONFIG block to account for the exact sampling instant in simulation.

Standard parameters

• Device ID selects which B-Box/B-Board to address when used in a multi-device configuration.
• Input channel (vectorizable) selects which physical input channel to read from (e.g. 0 to 15 on B-Box RCP).
• Use/load sensor parameters loads the  parameters of an imperix sensor.
• Sensor sensitivity (vectorizable) is the sensor sensitivity in Volts per measured unit (e.g. V/V for a voltage sensor and V/A for a current sensor).
• Sensor output offset (vectorizable) compensates for the sensor offset. It is expressed in Volts at the output of the sensor.
• Programmable gain value must match the configuration set on the frontpanel of the B-Box RCP. If the device is a B-Board PRO, it must be set to x2, to account for the +/- 5V input full-scale of the B-Board PRO (as opposed to +/- 10V on the B-Box RCP).

Advanced parameters

• Use ADC history enables the possibility the retrieve the N last sampled values.
• History depth (samples) is the number N of values to retrieve.

C++ functions

Standard functions

void Adc_ConfigureInput(unsigned int input, float gain, float offset, unsigned int device=0);
Code language: C++ (cpp)

float Adc_GetValue(unsigned int input, unsigned int device=0);
Code language: C++ (cpp)

Advanced functions for oversampling

These functions are used to perform oversampling, read Oversampling (PN154) to learn more.

void Adc_AddSamplingEvent(float phase);
Code language: C++ (cpp)

void Adc_ConfigureHistory(unsigned int input, unsigned int depth, unsigned int device=0);
Code language: C++ (cpp)

float Adc_GetHistory(unsigned int input, unsigned int n, unsigned int device=0);
Code language: C++ (cpp)

Example of use

This example considers the current sensor of a PEB8024 module. Its sensitivity is \(S=50.0\,[\text{mV/A}]\). As recommended in the datasheet, the chosen front-end gain is selected as \(G= 2\). Considering that the ADC offers 16 bits over the ±10V input range, this results in a total sensitivity \(\alpha = S\cdot G\cdot 32768/10=327.68\,[\text{bit/A}]\).

In this example, gain must therefore be equal to \(\mathtt{gain}=1/\alpha=3.052\,[\text{mA/bit}]\). The offset value can be adjusted empirically to cancel the measured value when no current is flowing through the sensor (static offset).

#define ADCONV (32768.0/10.0) // +/- 10V input range, 16-bit ADC
#define SENSITIVITY (0.05*2*ADCONV) // total sensitivity
#define I_GAIN (1.0/SENSITIVITY )
 
float I_meas = 0;
 
tUserSafe UserInit(void)
{
  Adc_ConfigureInput(0, I_GAIN, 0.0);
  return SAFE;
}
 
tUserSafe UserInterrupt(void)
{
  I_meas = Adc_GetValue(0);
  return SAFE;
}
Code language: C++ (cpp)