Sensoray 7429 User Manual
Page 19
Define Sensor
This command declares the type of sensor connected to a particular channel. Each sup-
ported sensor type is assigned a unique 8-bit sensor definition code. See the sensor ta-
bles near the end of this manual for a list of valid sensor definition codes.
Typically, this command is executed once for each channel during the host processor
initialization sequence (i.e., during power-on reset). Each execution declares the sensor
type for a single channel; hence, it is necessary to execute the command sixteen times
in order to set up all sixteen channels.
Any channel sensor having undeclared type will default to direct voltage in (500 µV/
bit). You should not attempt to declare an invalid sensor type. There are three varia-
tions of this command — proper command form is dictated by the sensor type:
All forms of this command begin the same way. The first command byte contains the
define channel sensor opcode and channel number. The second byte contains an ap-
propriate sensor definition code (a unique 8-bit value assigned to each valid sensor
type). This two-byte sequence is sufficient for most sensor types.
COMMAND:
(16 + CHAN),(SENSOR DEFINITION CODE)
RESPONSE:
NONE
Variation 2: Used to declare custom resistive sensor type (i.e., thermistors other than
Omega 44006 type 10K). This form is used only when specifying sensor definition
code 0CH. The 7429 will expect six additional bytes to follow the sensor definition
code. These additional bytes constitute the coefficients of a polynomial designed to
map sensor resistance into the desired output units. See the chapter on Custom Re-
sistive Sensors for more detailed information.
COMMAND:
(16 + CHAN),(0CH),
(HIGH COEFFICIENT MSB),(HIGH COEFFICIENT LSB),
(MID COEFFICIENT MSB),(MID COEFFICIENT LSB),
(LOW COEFFICIENT MSB),(LOW COEFFICIENT LSB)
RESPONSE:
NONE
Variation 3: When declaring a pressure gage/load cell sensor type, the 7429 will ex-
pect six additional bytes to follow the sensor definition code. The first two bytes con-
tain the gage mV/V rating times 10. The next two bytes specify the desired full-load
output data value. The last two bytes declare the gage input impedance in ohms.
COMMAND:
(16 + CHAN),(12H),
(V MSB),(V LSB),
(P MSB),(P LSB),
(R MSB),(R LSB)
RESPONSE:
NONE