What Is Integration; Pressure Reading Control - Honeywell PPT User Manual

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 is 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 PPT commands allow considerable flexibility in tailoring pressure acquisition times, sample
windows, thresholds, and output rates. These are controlled by 7 commands: Deadband and Sensitiv-
ity (DS), Integration (I=), Speed shift (S2), Speed shift at 50msec intervals (S5), Idle Count (IC),
Reading Rate (RR), and OPerating mode (OP). Figure 4.2 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 4.12and 4.13. 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.
The speed shift commands can only be enabled when the integration time is set using the I=Mn
form. When enabled, the thresholds for pressure change can be set that cause the output rate to
double (S2) or update at 50 msec intervals (S5). When the change of input pressure reaches or
exceeds the threshold, the sample rate shifts to the higher rate.
Second, the integration cycles may be spaced with idle periods that cause pressure reading times to
increase to as often as one every 51 minutes. The Idle Count (IC) command will insert, or 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
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
'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.
DS command can filter a small
RR and OP command modes when the
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