Section 10. Troubleshooting
example, if a sensor signal-to-data conversion is faulty, create a program that
only measures that sensor and stores the data, absent from all other inputs and
data. Write these mini-programs before going to the field, if possible.
10.3 Troubleshooting — Error Sources
Data acquisition systems are complex, the possible configurations endless, and
permutations mind boggling. Nevertheless, by using a systematic approach using
the principle of independent verification, the root cause of most errors can be
determined and remedies put into effect.
Errors are indicated by multiple means, a few of which actually communicate
using the word Error. Things that indicate that a closer look should be taken
include:
• Error
• NAN
• INF
• Rapidly changing measurements
• Incorrect measurements
These occur in different forms and in different places.
A key concept in troubleshooting is the concept of independent verification,
which is use of outside references to verify the function of dis-function of a
component of the system. For example, a multimeter is an independent
measurement device that can be used to check sensor signal, sensor resistance,
power supplies, cable continuity, excitation and control outputs, and so forth.
A very good place to start looking for trouble is in the data produced by the
system. At the root, you must be able to look at the data and determine if it falls
within a reasonable range. For example, consider an application measuring
photosynthetic photon flux (PPF). PPF ranges from 0 (dark) to about 2000
µmoles m
-–2
s
-–1
. If the measured value is less than 0 or greater than 2000, an
error is probably being introduced somewhere in the system. If the measured
value is 1000 at noon under a clear summer sky, an error is probably being
introduced somewhere in the system.
Error sources usually fall into one or more of the following categories:
• CRBasic program
o if the program was written completely by Short Cut, errors are very
rare.
o if the program was written or edited by a person, errors are much
more common.
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