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20.0.2 T8 Calibration Constants [T-Series Datasheet]

The T8 uses calibration constants to convert between the binary, used by hardware, and easier to understand units, typically volts.

Generally, users do not need to think about the calibration constants. The T8 automatically applies the calibration before reporting results. A couple exceptions are stream-mode and when the T8 has been instructed to return binary values. When using stream-mode, the calibration constants will be applied by the LJM driver.

The calibration constants are calculated as part of our new-unit test process. Those constants are then stored in the device's Internal Flash memory. The normal flash interface can be used to read the constants: (Internal Flash). Within flash, the calibration constants begin at memory address 0x687000, or in decimal format d6844416. The structure (location) of each calibration value can be seen in the C code snippet below.

T8 Calibration Values

typedef struct{
	float PSlope;
	float NSlope;
	float Center;
	float Offset;
typedef struct{
    uint32_t code;
    uint32_t reserved[7];
    uint32_t ain_type[8]; // 32 Contains type information for AINs.
    Cal_Set ain[8][11]; // 64 Calibration data for analog inputs.
    Cal_Set temp[8]; // 1472 Calibration data for temp sensors.
    Cal_Set VS; // 1600 Calibration data for VS measurement.
    Cal_Set IS; // 1616 Calibration data for IS measurement.
    Cal_Set dac[2]; // 1632 Calibration data for DACs
    float SecOSC_Freq; // 1664

The full size of the calibration section is 1668 bytes.

There are distinct sets of positive slope (PSlope), negative slope (NSlope), Center, and Offset values for each measurement.

For a given analog input x:

  • ain[x][0] for range ±11.000

  • ain[x][1] for range ±9.768

  • ain[x][2] for range ±4.884

  • ain[x][3] for range ±2.442

  • ain[x][4] for range ±1.221

  • ain[x][5] for range ±0.611

  • ain[x][6] for range ±0.305

  • ain[x][7] for range ±0.153

  • ain[x][8] for range ±0.076

  • ain[x][9] for range ±0.038

  • ain[x][10] for range ±0.019

Nominal Calibration Values

Analog inputs

Each AIN has 11 Cal_Sets, the nominal values for which are below:

{PSlope,                       NSlope,                        Center,       Offset},

{2.328872681E-006, -2.328872681E-006, 8388608, 19.536},

{1.164436340E-006, -1.164436340E-006, 8388608, -9.768},

{5.822181702E-007, -5.822181702E-007, 8388608, -4.884},

{2.911090851E-007, -2.911090851E-007, 8388608, -2.442},

{1.455545425E-007, -1.455545425E-007, 8388608, -1.221},

{7.277727127E-008, -7.277727127E-008, 8388608, -0.611},

{3.638863564E-008, -3.638863564E-008, 8388608, -0.305},

{1.819431782E-008, -1.819431782E-008, 8388608, -0.153},

{9.097158909E-009, -9.097158909E-009, 8388608, -0.076},

{4.548579454E-009, -4.548579454E-009, 8388608, -0.038},

{2.274289727E-009, -2.274289727E-009, 8388608, -0.019}

Temperature Sensors

{ -91.503268, 0, 0, 192.156863 };

Analog Outputs

{ 6243.64, 6243.64, 0, 800 };

Interval Converter

Vs { 0, 0, 0, 0 };

Is  { 0, 0, 0, 0 };

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