DATUM ELECTRONICS
M425 TORQUE TRANSDUCER HANDBOOK
12
HOW CHECKSUM IS CALCULATED:
The checksum is calculated and implements the CCITT 16-bit
CRC used by IEEE 802.15.4, using a Modulo 256 calculation.
A detailed description and software examples are available in
Technical Bulletin 1007.
SAMPLE RATES AND RESOLUTION
The M425 can output torque data at sample rates from 4 up
to 4000 samples per second. The lower data rates provide
resolution up to 1:560,000, at highest data rates the noise free
resolution reduces 1:11,000. See table 3 on page 13.
The sample rates that can be transmitted from the stator
to your instrumentation or computer are listed in tables 1
and 2 on page 13. These table show the rates for a range of
standard output strings.
PC PORT LIMITATIONS:
Note:
the M425 Transducer is capable of transmitting at the
rates above. Some PC’s have limited port configurations that
may not be able to cater for data rates at this level.
The maximum data rate at a given baud rate can be
calculated as: The basic string with a single torque value and
an RPM value has 22 characters, each character is 10 bits.
Therefore running serial communications at 9600 baud you
are limited to 43 samples per second (9600 ÷ (22 x 10).
By running at 115,200 baud this is increased to 525 samples
per second [115,200 ÷ (22 x 10)].
By sending the data in packets containing 10 torque values
the message becomes 94 characters long [115,200 ÷ (94
x 10)] as each packet contains 10 samples. The data rate
becomes 1225 samples per second.
