Operator`s manual

15 SERIAL INPUT
5
TABLE 2. Number of Characters/Output and Memory Requirementsfor Various Barometer
Output Modes
PARAMETER 5 The purpose of this parameter
is to limit the amount of time that Instruction
15 waits to receive a barometer output. If
the barometer fails to output, Instruction 15
advances to the next repetition or
instruction when the specified delay time
expires. If a barometer output is received,
Instruction 15 advances upon receipt of the
data, regardless of any remaining delay
time. Thus, the delay may be
overestimated without slowing instruction
execution. If the delay is underestimated,
or the barometer fails to output, a default
value of -99999 is placed in the specified
input location (PARAMETER 6).
One delay unit is approximately equal to
0.012 seconds. The required delay may be
estimated by dividing 0.012 into Instruction
15's execution time. Execution time is
dependent on both the hook-up
configuration and the barometer jumper
configuration. Exact execution time must
be verified, but an initial estimate may be
calculated as follows:
HOOK-UP CONFIGURATION #1:
ET = 0.1 x MA + .9
HOOK-UP CONFIGURATION #2:
ET = 0.1 x MA + .6
WHERE:
ET = Execution time in seconds
MA = Number of measurements averaged
The above equations overestimate the
execution time. When execution speed is
critical, the exact minimum execution time must
be determined through trial and error.
Parameter 5 Delay is estimated by:
Delay = ET/0.012
3.4 PROGRAM
The following example program assumes the
barometer is jumpered for TTL output and the
average of one measurement. The following
considerations are accounted for in the
program.
- To preserve the barometer measurement
resolution, barometer data must be output
to the 21X Final Storage in high resolution
(Instruction 78).
- A communication failure shows up as a
partial value or -99999. It is generally
desirable to exclude this value from
subsequent processing instructions and log
the incidence of failure. A failure may be
detected by comparing it to expected limits.
A bad value may be excluded from
processing by temporarily setting the
Intermediate Processing Disable flag (flag 9).