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20.0.1 T7 Calibration Constants [T-Series Datasheet]

The T7 automatically returns calibrated readings, so most people need not concern themselves with this section.

The factory applied calibration constants are stored in Internal Flash and can be accessed at any time through the use of the Modbus registers discussed in the parent to this section (Internal Flash section).

The calibration constants begin at memory address 0x3C4000, or in decimal format d3948544. The structure (location) of each calibration value can be seen in the C code snippet below. 

typedef struct{
	float PSlope;
	float NSlope;
	float Center;
	float Offset;
}Cal_Set;

typedef struct{
	Cal_Set HS[4];
	Cal_Set HR[4];

	struct{
		float Slope;
		float Offset;
	}DAC[2];

	float Temp_Slope;
	float Temp_Offset;

	float ISource_10u;
	float ISource_200u;

	float I_Bias;
}Device_Calibration;

The full size of the calibration section is 164 bytes, or 41 floats.  

The reason that there are 'Cal_Set's for each High Speed 'HS' and High Resolution 'HR', is that there are 2 analog converters on a T7-Pro.  A standard T7 uses only the High Speed analog converter, so only the HS[4] calibration values will be populated with valid information. A T7-Pro will have calibration information for both high speed, and high resolution converters.

Additionally, there are distinct sets of positive slope (PSlope), negative slope (NSlope), Center, and Offset values for each of the 4 gain settings on the device.

High speed AIN calibration values HS[4]:
HS[0] = calibration for gain x1
HS[1] = calibration for gain x10
HS[2] = calibration for gain x100
HS[3] = calibration for gain x1000

High resolution (-Pro only) AIN calibration values HR[4]:
HR[0] = calibration for gain x1
HR[1] = calibration for gain x10
HR[2] = calibration for gain x100
HR[3] = calibration for gain x1000 

Nominal Calibration Values

±10V Range:

  • Positive Slope: 0.000315805780
  • Negative Slope: -0.000315805800
  • Binary Center: 33523
  • Voltage Offset: -10.586956522

±1V Range:

  • Positive Slope: 0.000031580578
  • Negative Slope: -0.000031580600
  • Binary Center: 33523
  • Voltage Offset: -1.0586956522

±0.1V Range:

  • Positive Slope: 0.000003158058
  • Negative Slope: -0.000003158100
  • Binary Center: 33523
  • Voltage Offset: -0.1058695652

±0.01V Range:

  • Positive Slope: 0.000000315806
  • Negative Slope: -0.000000315800
  • Binary Center: 33523
  • Voltage Offset: -0.010586956

DACs:

  • Slope: 13200
  • Offset: 0

Temperature:

  • Slope: -92.6
  • Offset: 467.6

Current Sources:

  • 10 μA: 0.000010
  • 200 μA: 0.000200

AIN Bias Current: 0.000000015