Sensoray 118 - Manual (Page 23)

Sensoray Model 118 Smart A/D™ Instruction Manual 21 Commands: Channel Configuration
6.2.4 SetCoefficients
Defines linearization coefficients for a channel that was
previously declared for sensor type Custom Resistive
Sensor (CRS).
Three coefficients are specified. The three values belong
to a polynomial of the following form:
The Smart A/D™ measures CRS channels by performing
an autoranging measurement of the sensor resistance.
The measured resistance is then transformed into
user-defined units by means of the above second-degree
polynomial expression. The resulting value is converted
to a 16-bit integer and stored in onboard memory. This is
the value that is returned to the host when the
GetSensorData or GetAllSensors commands are
executed.
Declaring a channel as type CRS is practical for resistive
sensors subject to the following constraints:
• Sensor resistance must not exceed the maximum
resistance that can be measured by the Smart A/D™.
• A quadratic linearization polynomial is sufficiently
accurate for the application.
Each coefficient is expressed in the 4-byte form used
internally by the Smart A/D. The the
SendReal function
(see Section 5.3) takes care of translating the coefficients
into the required internal format.
Driver
// Set the coefficients for the specified channel. The coefficients are
// passed to the driver function through an array.
VOID SetCoefficients( USHORT BasePort, UCHAR Channel, DOUBLE *pCoeffs )
{
SendByte( BasePort, Channel | CMD_SET_COEFFS );
for ( USHORT nCoef = 0; nCoef < 3; nCoef++ )
SendReal( BasePort, *pCoeffs++ );
}
Example
// Set the coefficients for channel 2, which is connected to a linear slide
// potentiometer whose position, P, is a function of resistance, R, as
// follows: P = -0.0023 * R^2 + 12.6 * R + 0.45. After executing this command,
// the GetSensorData and GetAllSensors commands will return the value P from
// this channel in the form of a signed 16-bit integer.
DOUBLE Coeffs[] = { -0.0023, 12.6, 0.45 };
SetCoefficients( MyBasePort, 2, Coeffs );
Command: (192 + Chan),(A0),(A1),(A2),(A3),(B0),(B1),(B2),(B3),(C0),(C1),(C2),(C3)
Response: None
f R
( )
aR 2 bR c + + =