
12
4.2 What Is Integration?
The input pressure is converted to an analog electrical signal at the pressure sensor. This signal feeds into a delta-
sigma analog-to-digital (A/D) converter where it is changed into a digital signal representing the pressure value.
During the A/D conversion cycle, the signal is integrated over time. That is, the pressure reading is averaged
(integrated) over the A/D conversion cycle so the resultant digital value is the summation of the average pressures
observed during the cycle. This conversion cycle can be controlled by the user with the Deadband and Sensitivity
(
DS
), Synchronization Integration (
SI
), Idle Count (
IC
), and Integration (
I=
) commands.
4.3 Pressure Reading Control
The HPB commands allow considerable flexibility in tailoring pressure acquisition times, sample windows, thresholds,
and output rates. These are controlled by five commands: Deadband and Sensitivity (
DS
), Integration (
I=
), Idle Count
(
IC
), Reading Rate (
RR
), and OPerating mode (
OP
). Figure 2 illustrates how the user may control these attributes in
three ways:
First,
the internal analog-to-digital converter integration time may be controlled over a range of 1 sample every 12
seconds up to 120 samples per second. This is controlled using the Integration (
I=
) command. The integration time
is used to control the A/D integration cycle that allow noisy pressure inputs to be filtered, or averaged, over a
selected period of time. See Figures 5. The integration time can be set within a range of 1 to 120 samples/sec using the
I=Rn
form or a range of 100msec to 12 sec/sample using the
I=Mn
form. The values for n range from 1 to 120 for
both the rate (
Rn
) form and the millisecond (
Mn
) form.
Second,
the integration cycles may be spaced with idle periods that cause pressure reading times to increase to only
as one every 51 minutes. The Idle Count (
IC
) command will skip from 0 to 255 idle periods equal to the
integration time. If the integration time is set to the maximum, 12 sec/sample, and an idle count of 255 is selected, then
the time between samples = 12 sec. x 256 = 51.2 minutes.
Third,
the reading rate may be controlled so pressure readings are obtained only when pressure changes occur. The
Reading Rate (
RR
) command can be set to output only changed readings, or skip from 100 to 1000 identical readings.
The Operating Mode command (
OP
) can be set to output every reading or to only output changes. The Deadband
setting in the
DS
command can filter a small pressure change by not allowing the pressure reading to vary as long as
it remains within the deadband limits. This controls the sensitivity to change of the
RR
and
OP
command modes
when the output only when pressure changes options are selected. If the pressure signal is stable within the
deadband limit, then the pressure reading time can be increased up to 1000 times the integration time by using the
RR
command.