Instrumentation & Measurement Magazine 25-7 - 7

Remembering Old Practices to
Validate Measurement Data
Vítor Viegas, J. M. Dias Pereira, Pedro M. B. Girão, and Octavian Postolache
M
easurement data only becomes information if it
is credible and useful. Usefulness is something
hard to judge because it depends on who is going
to use the data (the consumer) and for what purpose (the
end application). Credibility, in turn, is easier to assess because
it mostly depends on the conditions in which the data
was acquired. If the measurement chain is working properly,
including sensors, signal conditioning circuits, and analog-todigital
converters, then it is very likely that the data is valid.
As a rule of thumb, we can rely on the data if the measuring
method is adequate, and all the instruments involved in the
measuring procedure are working fine.
In this paper we revisit two ways to monitor the health of
measurement equipment (and thus the health of the measured
data). The first approach is based on status registers and service
requests as defined by
the Hewlett-Packard (HP)
in the 1960s and later adopted
by the IEEE 488 and
1451 Standards. The second
approach is based on status
bits and safety locks as
defined by fieldbus manufacturers
in the 1990s. Both
approaches have proved
to be effective in monitoring
the health of measured
data and can provide important
guidelines for the
future, especially now that
systems have entered the
IoT era.
Status Registers
and Service
Requests
Status registers have been
used for many years to
keep track of what is going
October 2022
on inside the measurement instrument. Fig. 1 illustrates the
working principle of a status register, including the status register
itself, the interrupt mask, and the connection between the
measurement instrument and an external computer.
The status register contains bits that act as flags to signal a
given condition of the instrument. Usually, the status bits are
written by the internal circuitry of the instrument and can only
be read from the external computer using the communication
interface (in other words, status bits are typically read-only).
To prevent the computer from polling the status register permanently,
a programmable interrupt mechanism is installed in
addition to notify the computer whenever a given condition
is met. The mechanism includes a mask register, several AND
gates, and one OR gate. The mask bits are AND-wired with the
status bits, one by one, so that a mask bit equal to '0' disables
Fig. 1. Working principle of a status register.
IEEE Instrumentation & Measurement Magazine
1094-6969/22/$25.00©2022IEEE
7

Instrumentation & Measurement Magazine 25-7

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 25-7

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