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ADS-14221, PPT2 User Manual
4.0 Terminology
simplified block diagram
Pressure And
Pressure
Temperature
Input
Bridge Circuits
4.1
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), Idle Count (IC), and
Integration (I=) commands.
4.2
PRESSURE READING CONTROL
The PPT2 commands allow considerable flexibility in tailoring pressure acquisition times, reading
windows, thresholds, and output rates. These are controlled by 4 commands: Deadband and
Sensitivity (DS), Integration (I=), Idle Count (IC), and OPerating mode (OP). The user may control
these attributes in three ways:
First, the internal integration time may be controlled over a range of 1 reading every 10 seconds up
to 1000 readings per second. This is controlled using the 'Integration' (I=) command. Pressure values
are calculated every millisecond. The integration time is used to control the amount of averaging of
these pressure values to create each pressure value. The integration time can be set within a range
of 1 to 1000 readings/sec using the I=Rn form, or a range of 10 msec to 10 sec/reading using the
I=Mn form. The values for 'n' range from 1 to 1000 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 as long as one every 42.67 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,
10 sec/reading, and an idle count of 255 is selected, then the time between readings = 10 sec. x 256
= 42 minutes, 40 seconds.
Third, the reading rate may be controlled so pressure readings are obtained only when pressure
changes occur. The OPerating mode command (OP) can be set to output every reading (OP=A) or
to only output changes (OP=U). The Deadband setting in the DS command can filter a small
pressure change by not allowing the pressure output reading to vary as long as it remains within the
PPT2
Analog
to Digital
Converter
Raw Pressure and Temperature "Samples"
Corrected Pressure and Temperature "Values" or
Averaged Corrected Pressure and Temperature "Values"
Pressure and Temperature "Readings"
or Pressure and Temperature "Output"
Power
Regulation
Micro-
RS-232 or
processor
RS-485
Transceiver
RAM
EEPROM
16-bit Digital
to Analog
FLASH
Converter
October, 2016
DC
Input
Digital
Serial
Data
0-5V
Output
17 of 85
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