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Transformations

ADC Transformations

The six ADC channels are passed through a transformation stage before being output as JCS signals

Select a transformation by writing an enum to transform_type:

Control mode Description
linear_gain_offset Basic gain and offset transform.
linear_gain_offset_tc_adc Gain and offset transform with temperature compensated ADC values.
linear_gain_offset_tc_mat Gain and offset transform with temperature compensated gain matrix and offset vector.

Gain and offset

Basic linear transform of the form \(\mathbf{y} = \mathbf{Ax} + \mathbf{b}\).

Where

  • \(\mathbf{x}\) is vector of 6 ADC values in the range [-1, 1]
  • \(\mathbf{A}\) is a 6x6 gain matrix
  • \(\mathbf{b}\) is a 1x6 offset vector

Configure the transform with:

Commands Type Required Description
transform_gain_offset_A float32 Required Float32 vector of gain matrix coefficients.
Length: 36
transform_gain_offset_b float32 Required Float32 vector of offset vector coefficients.
Length: 6

Gain and offset, with temperature compensated ADC

Gain and offset transform with temperature compensated ADC values, of the form \(\mathbf{y} = \mathbf{Ax}(t_c) + \mathbf{b}\)

  • \(\mathbf{x}(t_c)\) is vector of 6 temperature compensated ADC values in the range [-1, 1]
  • \(t_c\) is the temperature from the source defined in temperature_source
  • \(\mathbf{A}\) is a 6x6 gain matrix
  • \(\mathbf{b}\) is a 1x6 offset vector

Configure the transform with:

Commands Type Required Description
transform_gain_offset_tc_adc_A float32 Required Float32 vector of gain matrix coefficients.
Length: 36
transform_gain_offset_tc_adc_b float32 Required Float32 vector of offset vector coefficients.
Length: 6

Per ADC channel temperature compensation

Each ADC channel may be temperature corrected as:

\(x(t_c) = x - bias(t_c)\) ,

where \(x\) is the ADC value and \(bias(t_c)\) is the polynomial:

\(bias(t_c) = C_{0}dt^3 + C_{1}dt^2 + C_{2}dt + C_{3}\)

and

\(dt = t_c - (t_{c-max} - t_{c-min})\) .

Here \(C_0\) to \(C_3\) are the temperature compensation polynomial coefficients and \(t_{c-max}\) and \(t_{c-min}\) define the temperature region over which the polynomial coefficients were captured. This also defines the valid compensation range. If the temperature exceeds the valid compensation range the temperature compensation action will clamp at that limit and the Temperature compensation clamped flag (bit 4) in the JCS op_state signal will be asserted.

Valid signal outputs will still be generated, however the correctness of the signals cannot be assured.

Configure the polynomial coefficients and temperature range with:

Commands Type Required Description
transform_gain_offset_tc_adc_x_poly_0 float32 array Required Float32 vector of ADC compensation polynomial coefficients for channel 0.
Length: 4
transform_gain_offset_tc_adc_x_poly_1 float32 array Required Float32 vector of ADC compensation polynomial coefficients for channel 1.
Length: 4
transform_gain_offset_tc_adc_x_poly_2 float32 array Required Float32 vector of ADC compensation polynomial coefficients for channel 2.
Length: 4
transform_gain_offset_tc_adc_x_poly_3 float32 array Required Float32 vector of ADC compensation polynomial coefficients for channel 3.
Length: 4
transform_gain_offset_tc_adc_x_poly_4 float32 array Required Float32 vector of ADC compensation polynomial coefficients for channel 4.
Length: 4
transform_gain_offset_tc_adc_x_poly_5 float32 array Required Float32 vector of ADC compensation polynomial coefficients for channel 5.
Length: 4
transform_gain_offset_tc_adc_tC_max float32 Required Maximum temperature at which compensation is valid.
transform_gain_offset_tc_adc_tC_min float32 Required Minimum temperature at which compensation is valid.

Temperature compensation

The temperature compensation source may be configured by writing an enum to temperature_source:

Source Description
source_temperature_disabled The temperature compensation is disabled.
Default
source_temperature_onboard Temperature is sourced from the on board temperature sensor. This effectively measures the temperature of the device PCB.
source_temperature_an_0 External analog temperature sensor attached to port an_0. An example is a sensor fixed to, or in the vicinity of the strain gauge elecment.
The analog interface must have the gain and scale configured correctly.
source_temperature_network Temperature is sourced from the the JCS network. Input signal t_net must be connected to a valid temperature source