Introduction; Product Overview; Hardware Description; Table 1.1 Various Digital And Analog Output Modes - Honeywell PPT User Manual

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INTRODUCTION

1.1

PRODUCT OVERVIEW

The Honeywell Model PPT and PPTR Precision Pressure Transducers (PPT) provide high accuracy
pressure readings in both digital and analog form. The first-time user will be able to use the PPT
within minutes, yet capability exists to configure the PPT for optimum performance in specific
applications. Throughout this User's Manual, both the PPT and PPTR will be referred to as PPT
(Precision Pressure Transducers) unless the specific model number is stated.
The heart of the PPT measuring system is a silicon piezoresistive sensor which contains both pres-
sure and temperature-sensitive elements. Digital signals representing temperature and pressure are
processed by a microprocessor to produce fully temperature compensated and calibrated pressure
readings over the entire -40 to 85 °C temperature range. The output modes are shown in Table 1.1.
The PPT receives commands and sends data from either a RS-232 port or a multidrop RS-485 port.
Using the RS-232 type PPT, up to 89 units can be connected in a ring configuration to a single serial
port of a computer. The RS-485 type PPT allows up to 89 PPTs to be connected to a two-wire
multidrop bus, when bus repeaters are used to satisfy the RS-485 bus electrical requirements. Group
(multicast) addressing allows up to nine groups of PPTs to be addressed with a single command.
Global (broadcast) addressing will send a command to all PPTs on the serial bus. Any computer
having a serial port and terminal emulation software can be connected to the PPT to allow the user
to select baud rates, sample rates, readout resolution, units of pressure and other choices.
Analog output from the 12-bit digital-to-analog converter may be obtained without a host computer.
User selected functions may be set through the digital interface. The selected functions may either
be used temporarily, until the PPT is powered down, or may be stored in the internal EEPROM to
automatically configure the PPT each time power is applied.
Both the analog and digital outputs are corrected digitally over the full range of -40 to 85 °C. The
PPT has a typical accuracy of 0.05% of full scale (FS) and the PPTR has a typical accuracy of 0.10%
FS. Note that full scale for a 20 psig and a 20 psia is 20 psi, but for a 20 psid it is 40 psi. This is
important to note when determining the accuracy allowance.
Digital Output
Single or Continuous Pressure Readings
Single or Continuous Temperature Readings
Single or Continuous Remote PPT Values
1.2

HARDWARE DESCRIPTION

See Sections 8 and 9.
Table 1.1—Various Digital and Analog Output Modes
Analog Output
Single Pressure Analog Voltage
Tracking Pressure Analog Voltage
User Set Analog Voltage
Remote PPT Controlled Voltage
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