Honeywell PPT, PPTR User Manual

Honeywell Precision Pressure Transducers

PPT and PPTR User’s Manual

ADS-14052, Revision B, 10/16

Email: [e-mail]
Web: www.pressuresensing.com

No part of this manual may be reproduced or transmitted in any form or by any means, electronic or mechanical, including
photocopying and recording, for any purpose, without the express written permission of Honeywell, Inc. Honeywell
reserves the right to make changes to any products or technology herein to improve reliability, function or design.
Honeywell does not assume any liability arising out of the application or use of any product or circuit described herein;
neither does it convey any license under its patent rights nor the rights of others.

PPT User’s Manual

Contents

0 USER MANUAL CONTENT ..................................................................................... 1

1 INTRODUCTION ....................................................................................................... 2

1.1 Product Overview ............................................................................................ 2

1.2 Hardware Description .................................................................................... 2

2 GETTING STARTED ................................................................................................. 3

2.1 Overview .......................................................................................................... 3

2.2 Equipment Needed ......................................................................................... 3

2.3 Terminal Program Settings ............................................................................ 3

2.4 Initial Turn-On Response ............................................................................... 4

2.5 Command Format ........................................................................................... 4

2.6 Step-By-Step Examples .................................................................................. 5

2.7 Command Functional Groups ........................................................................ 7

3 COMMANDS - QUICK REFERENCE ...................................................................... 9

4 FUNCTIONAL OPERATION .................................................................................... 13

4.1 Overview .......................................................................................................... 13

4.2 What Is Integration? ....................................................................................... 14

4.3 Pressure Reading Control ............................................................................... 14

4.4 Output Voltage Control ................................................................................... 16

4.5 Pressure Window Control ............................................................................... 16

4.6 Customized Pressure Range ........................................................................... 17

4.7 Setting Pressure Set Points ............................................................................ 18

4.8 PPT Analog Output Configurations ............................................................... 19

4.9 Command Illustrations ................................................................................... 20

4.10 Pressure Reading Decimal Position ............................................................... 24

4.11 PPT Addressing ............................................................................................... 25

i

PPT User’s Manual

Contents (cont’d)

5 COMMANDS .............................................................................................................. 28

5.1 Command Format ........................................................................................... 28

5.2 Information Request Commands ................................................................... 29

5.3 Action Directing Commands ........................................................................... 29

5.4 Command Replies—General .......................................................................... 29

5.5 ASCII Format Replies ..................................................................................... 30

5.6 Binary Format Replies ................................................................................... 31

5.7 Command And Reply Sequencing .................................................................. 34

5.8 Command Errors ............................................................................................. 35

5.9 Command Summary Table ............................................................................. 37

5.10 Command Descriptions ................................................................................... 39

6 ELECTRICAL CONNECTIONS ................................................................................ 73

7 TIMING DIAGRAMS ................................................................................................. 75

8 SPECIFICATIONS ..................................................................................................... 78

9 DIMENSIONS ............................................................................................................ 80

ii

Figure 4.1

Figure 4.2

Figure 4.3

Figure 4.4

Figure 4.5

Figure 4.6

Figure 4.7

Figure 4.8

Figure 4.9

Figure 4.10

Figure 4.11

Figure 4.12

Figure 4.13

Figure 4.14

Figure 4.15

Figure 4.16

Figure 4.17

Figure 4.18

Figure 4.19

Figure 4.20

Figure 4.21

Figure 5.1

Figure 5.2

Figure 6.1

Figure 6.2

Figure 6.3

Figure 6.4

Figure 6.5

Figure 7.1

Figure 7.2

Figure 7.3

Figure 7.4

Figure 7.5

Figure 7.6

Figure 9.1

Figure 9.2

Figure 9.3

Figures

PPT Block Diagram .......................................................................................... 13

Pressure Reading Control ................................................................................ 15

Factory Set Output Levels ............................................................................... 16

User Modified Output Levels ........................................................................... 17

User Modified Pressure Span .......................................................................... 17

Custom Slope (X=) Options .............................................................................. 17

Custom Offset (Z=) Options ............................................................................. 17

Pressure Set Point Set ..................................................................................... 18

Deadband on Set Point ..................................................................................... 18

PPT Pressure to Analog Voltage ...................................................................... 19

PPT Pressure Readings and Analog Voltage Control ..................................... 19

Sensing Remote Analog Pressure .................................................................... 19

Integration (I=) Command, Example 1 ........................................................... 20

Integration (I=) Command, Example 2 ........................................................... 21

S2 Speed Shift Command Example ................................................................. 21

S5 Speed Shift Command Example ................................................................. 22

Deadband and Integration (DI) Command Examples ........................... 22 – 23

Idle Count (IC) Command Example ................................................................ 23

Synchronize Integration Cycles (SI) Command Example .............................. 24

RS-232 PPT Ring Network .............................................................................. 25

RS-485 PPT Multidrop Network ..................................................................... 26

Single PPT Command and Reply .................................................................... 34

Multiple PPT Network Command and Replies ............................................... 35

PPT Electrical Connector Pin Assignments .................................................... 73

Connection for RS-232 Operation and Analog Output ................................... 73

Connection for RS-485 Operation and Analog Output ................................... 74

Connection for Analog Output and Battery Operation ................................... 74

Connection for Computer Operation and

User Controlled Analog Voltage Output ...................................................... 74

Default Single Pressure Reading Timing Diagram ........................................ 75

Default Continuous Pressure Reading Timing Diagram ................................ 75

Continuous Pressure (with IC = 1) Timing Diagram ...................................... 75

Timing Diagram for 20 Readings Per Second ................................................. 76

Timing Diagram for 50 Readings Per Second ................................................. 76

Timing Diagram for 120 Readings Per Second ............................................... 76

PPT Case Outline ............................................................................................. 80

Electrical Connector ......................................................................................... 80

PPTR Case Outline .......................................................................................... 81

iii

Table 1.1

Table 4.1

Table 4.2

Table 5.1

Table 5.2

Table 5.3

Table 5.4

Table 5.5

Table 7.1

Table 7.2

Table 9.1

Table 9.2

Table 9.3

Tables

Various Digital and Analog Output Modes ........................................................... 2

PPT to PPT Remote Sensing Setup Commands ................................................. 20

Decimal Place Locations for Pressure Readings ................................................ 24

Header Description for Binary Format Pressure Readings .............................. 31

Binary Format Character Codes ......................................................................... 33

Command List ..................................................................................................... 37

Command Factory Default List .......................................................................... 39

Display Units Options ......................................................................................... 47

Transmission Times at Selected Baud Rate ....................................................... 77

Number of Bytes in Various Replies ................................................................... 77

ASCII Conversion Table ...................................................................................... 81

RS-232 Standard Pin Connections ..................................................................... 81

Electrical Signal Levels ....................................................................................... 81

iv

0 USERS MANUAL CONTENT

This user’s manual is divided into the following sections.

Section 1 Introduction—Product overview and hardware description.

Section 2 Getting Started—Lists equipment and procedures necessary to operate the PPT

and provides a few simple command examples, which will get first-time users
acquainted with the command structure.

Section 3 Commands: Quick Reference—A brief description of each command with

typical PPT input and response examples.

Section 4 Functional Operation

Section 5 Commands—Contains a detailed description of the command structure, func-

tional groupings and all user commands.

Section 6 Electrical Connections—Contains wiring diagrams for various PPT electrical

connections.

Section 7 Timing Diagrams—Illustrates RS-232 serial port timing for command and

reply interaction.

Section 8 Specifications—Contains electrical and environmental specifications.

Section 9 Dimensions—Contains a case outline of the PPT

It is suggested that the first-time user read the “Getting Started” section to be sure the necessary
items are on hand. PPTs are available in various pressure ranges for absolute, gauge and differential

modes of operation. Be sure to connect a source of pressure that matches the transducer range and mode.

1

1 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 pres­sure 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

Analog Output

Single or Continuous Pressure Readings

Single or Continuous Temperature Readings

Single or Continuous Remote PPT Values

Table 1.1—Various Digital and Analog Output Modes

1.2 HARDWARE DESCRIPTION

See Sections 8 and 9.

Single Pressure Analog Voltage

Tracking Pressure Analog Voltage

User Set Analog Voltage

Remote PPT Controlled Voltage

2

2 GETTING STARTED

2.1 OVERVIEW

The first-time user should approach the PPT in a manner analogous to using a word processor
program; i.e., many features are available but one may begin by using those of interest at the mo­ment. Section 2.7 of this manual lists command features by functional groups to assist in this selec­tion. When shipped from the factory, the default settings provide a pressure transducer that will be
usable for many applications. Once the user is familiar with the performance and command struc­ture, changes may be made and stored using the ‘Store Parameters’ (SP) command. Once stored, the
new default settings are activated each time the PPT is powered up. This tailors the personality of
the PPT to meet the needs of a particular application.

2.2 EQUIPMENT NEEDED

To prepare the PPT for operation, three items are needed:

• A mating connector with proper wiring connections (see connector part number and wiring
diagram in Section 6—Electrical Connections);

• A DC power supply;

• A source of pressure that is properly matched to the range and type of the PPT.

To operate the PPT in the analog output mode, one additional item is needed:

• Voltage Output - A five digit voltmeter with 0-5 volt range connected between Analog Out and
Signal Common. A computer is not required when operating in this mode.

To operate the PPT in the digital output mode, one additional item is needed:

• A computer, or host processor, having an RS-232 or RS-485 serial port and terminal program
software such as PROCOM™, VERSATERM™, TERMINAL (Windows

HYPERTERMINAL (Windows

®

95). These programs are normally used to interface to a modem.
The wiring diagram designates which PPT pins must connect to the computer “send”, “receive”
and “common” pins for proper communications. Some computers may not have an RS-232 or RS­485 serial port connection identical to the one shown in Section 6, making it necessary to adapt
the PPT connections to that particular computer.

2.3 TERMINAL PROGRAM SETTINGS

• Enter the following settings in the terminal program:

Baud Rate .... 9600

Start Bits .... 1

Data Bits .... 8

Stop Bits .... 1

Parity .... None

• Attach a line feed to the carriage return.

• Turn the local echo ON.

When shipped from the factory, the PPT is set to a baud rate of 9600, 1 start bit, 8 data bits with no
parity and one stop bit. If the baud rate has been subsequently changed, and is unknown, it will be
necessary to search all baud rate values to reestablish communication. See the BP command descrip­tion in Section 5.10 of this manual for possible settings.

3

®

3.x) or

2.4 INITIAL TURN-ON RESPONSE

Analog Output

The analog output will provide a voltage (range 0-5V) which, when no pressure is applied to the
PPT, reads:

Pressure Type

Gauge units

Differential units

Absolute units

Digital Output

Once the wiring connections and terminal program settings are complete, the PPT will automati­cally send the following response (or similar to) when power is applied. This reply will be gener­ated any time power is applied to the PPT.

Typical Reply:

RS-232 ?01PPT____10__psid

RS-485 ?00PPT____10__psid

The “?01” or “?00” indicates a default address device called a “null address”. This PPT has not yet
been assigned an ID number so it assumes the null address. The “PPT____10__psid ” indicates a
10 psi differential device.

2.5 COMMAND FORMAT

Any command interaction with the PPT requires electrical connection to the RS-232 or RS-485
serial communications pins. There are two basic types of commands – action directing commands

and information requesting commands. Theses are described in
Commands – Section 5.

Typical PPT commands have the form *ddcc = nnn <cr>

Voltage Output

(@ zero applied pressure)

0 volt

2.5 volts

A voltage representing atmospheric pressure

Where: *

dd
cc

=
nnn
<cr>

is the command header character
is the decimal address of the PPT
is a command (refer to Commands – Section 5 for a complete

description of commands)
equal sign (required in some commands)
additional characters (required in some commands)
carriage return is required to end all commands
(do not type, press the ENTER/RETURN key)

4

2.6 STEP-BY-STEP EXAMPLES (Only for single PPT connection)

READ SINGLE PRESSURE

Once the PPT is powered up and connected to a computer, enter the following command:

Type: *00P1 <cr> Response: ?01CP=15.458 (for RS-232)

?00CP=15.458 (for RS-485)

where * indicates the start of a command

00 is the null address of the PPT (see note below)
P1 is the command to read the most current pressure

Note: The “?” indicates a response from a null address PPT – one which has not been assigned a
device ID. A null address, 00, is coded into each PPT at the factory. When a RS-232 null address

PPT responds, it adds one to its address, hence, the response ‘01’. Refer to the ID command in
Appendix A for a description of addresses and responses.

In the reply, the “01” identifies the individual unit address (range 01-89). The “CP=15.458”
indicates a compensated pressure of 15.458 psi. Your unit may not show this specific reading,
depending on the applied pressure it is measuring.

SET DEVICE ID

To give the PPT an assigned address of 01 up to 89, enter the following commands:

Type: *00WE <cr> This enables the PPT to change a parameter in RAM

Type: *00ID=01 <cr> This sets the null addressed PPT to device ID=01.

Note: The device ID is now used in the command input

Type: *01S= <cr> Response: #01S=00052036 (serial number test)

The “#” now replaces the “?” in the header and indicates the PPT
response is from an address assigned unit.

where: * indicates the start of a command

00 is the null address of the PPT

W E is the command to enable a configuration parameter change

I D is the command to change the device address

01 is the assigned PPT address for this example

S= is the command to read the serial number

READ PRODUCTION DATE

To read the production date, enter the following command:

Type: *01P= <cr> Response: #01P=04/13/95

5

READ CONTINUOUS PRESSURE

For continuous pressure readings at the factory set default rate of 5 per second, enter the follow­ing command:

Type: *01P2 <cr> This enables a continuous stream of compensated pressure readings

to flow into the terminal program.

Type: $*99IN <cr> This is the best way to stop the continuous pressure reading com-

mands. The ‘$’ character temporarily stops, or suspends, either the
continuous pressure or temperature readings. The *99IN command
stops the continuous pressure readings.

CHANGE TO A NEW SAMPLE RATE

Enter the following command:

Type: *01WE <cr> This enables the PPT RAM to accept a changed parameter.

Type: *01I=M20<cr> This sets the integration time to value 20, which corresponds to an

output sample every 2 seconds.

The sample rate will change to one every 2 seconds. I= is an abbreviation for Integration time
which determines how long to accumulate pressure samples between readings. Each integration
period gathers the data for one pressure reading output (see Section 4.2 What is integration?).
The range of integration times can be set by specifying readings per second (I=R45 for 45 read­ings/sec) or time delay in 100 millisecond intervals (I=M60 for 6 seconds). The factory set inte­gration time is 5 samples per second (I=M2).

The output data rate can also be altered by use of the idle count (IC) command or by changing
the reading rate (RR) command in conjunction with the operating mode (OP) command. See
Section 4 for description of these commands.

REPEAT THE READ CONTINUOUS PRESSURE STEP ABOVE

Notice the slower output rate of one sample every 2 seconds.

TRY OTHER COMMANDS

Experiment with other commands to become familiar with the command structures. A short
overview of each command with input and response examples is shown in Section 3 Commands –

Quick Reference. See Section 5—Commands for complete command descriptions. Until an
SP=ALL command is executed, no changes will be stored in the EEPROM. Re-apply the power
or send an IN=RESET command to revert to EEPROM default settings.

6

2.7 COMMAND FUNCTIONAL GROUPS

PRESSURE DISPLAY UNITS PPT reads out psi, in wc, mm Hg, etc.

D U Set pressure units for output readings—any one of 13 common units

U = Specify a user supplied unit of measure

TEMPERATURE

T1 Single °C
T2 Continuous °C
T3 Single °F
T4 Continuous °F

RS-232/RS-485 BUS PARAMETERS

BP Changes baud rate and parity

I D Assign device ID and group addresses

M = Select alternate message Headers [RS-485 only]

SI Synchronize Integration cycles among units [RS-485 only]

TO Set Transceiver Operating parameters

OUTPUT READING AND RATE Speed up or slow down output rate

Single Reading Commands

P1 Single RS-232 pressure reading...ASCII format
P3 Single RS-232 pressure reading...binary format
T1 Single RS-232 temperature reading...°C

T3 Single RS-232 temperature reading...°F

Continuous Readings Commands

P2 Continuous RS-232 pressure readings...ASCII format
P4 Continuous RS-232 pressure readings...binary format
T2 Continuous RS-232 temperature readings...°C

T4 Continuous RS-232 temperature readings...°F

Integration Time Commands —Changes pressure reading response time

DS Set deadband and sensitivity parameters

I = Set pressure integration time, and reading rate
S2 Set threshold level for 2X speed shift
S5 Set threshold level for output within any 50 msec period

SI Synchronize pressure Integration cycles

Idle Count Command —Changes pressure reading response time

I C Set number of idle integration cycles

Reading Response To Changes In Input Pressure—Filters small changes

S2 Set threshold level for 2X speed shift
S5 Set threshold level for output within any 50 msec period

RR Set number of identical readings to skip
OP Transmit all readings or only changed readings

FORMAT PRESSURE READINGS—Changes data length into host processor

Binary Format Commands

P3 Single RS-232 pressure...binary format
P4 Continuous RS-232 pressure...binary format

OP Set operating mode...binary format checksum...set signed or extended binary output

format

ASCII Format Commands

All readings, except P3, P4 and ~, are ASCII format readings.

OP Set operating mode...all readings or only changed readings

7

START-UP PARAMETERS—Sets the PPT configuration after power is applied

WE Enable parameter writes to the RAM or EEPROM

SP Store RAM parameters to the EEPROM for startup

M O Specify the power-up message and operating mode

PRESSURE NOISE REDUCTION—Reduces pressure noise signals

DS Set deadband and sensitivity parameters

ANALOG OUTPUT

D A Enables PPT sensed pressure to control the analog output

N E Enable host computer control of the analog output

N = Supply an analog output value in ASCII format, by host computer

~ Supply an analog output value in binary format, by host computer

H = Set the analog highest reading FS voltage

L = Set the analog lowest reading voltage

O= Set pressure window offset for minimum analog reading

W= Set pressure window width for analog full scale span

A N Turn on or off the customized H=, L=, O=, and W= analog scales

DIAGNOSTIC AND RESET CONTROL

I N Performs a software reset of microprocessor
RS Read status of error indicators
C K Performs and provides the result of EEPROM checksum
OP Use pressure reading checksum for binary format

OFFSET TARE CONTROL

T= Allows user to install an offset in the output reading
TC Turn on or off user controlled tare function

USER AND STARTUP MESSAGES

A= Store 8 characters of user supplied data
B= Store 8 characters of user supplied data
C= Store 8 characters of user supplied data, which can be configured as a watchdog or

reset message

D= Store 8 characters of user supplied data, which can be configured as a watchdog or

reset message

M O Specify the startup header selection

PPT UNIT INFORMATION

P= PPT production date

S= PPT serial number
V= PPT software version number

I D Assign device ID and group addresses

M = Read the maximum full scale pressure limit allowed

CUSTOMIZE PRESSURE WINDOW

F= Customize the full scale pressure limit
O= Set pressure window offset for minimum analog reading

W= Set pressure window width for analog full scale span

X= Set the slope “m” parameter for user input mx+b control
Y= Same as X= but for negative slope in differential device

Z= Set the offset “b” parameter for user input mx+b control

8

3 COMMANDSQUICK REFERENCE

A N Analog Range Setting

A= Data String A

(up to 8 characters, a <cr> indicates end-of­message. More than 8 characters is an invalid write)
(Can store info. such as dates, readings, etc.)

B P Baud Rate and Parity Setting

B= Data String B

(up to 8 characters, a <cr> indicates end-of-message,
and more than 8 characters will not write to location)
(Can store info. such as dates, readings, etc.)

C K Check EEPROM

C= Data String C

(up to 8 characters, a <cr> indicates end-of-message,
and more than 8 characters will not write to location)
The C and D string can be used for a watchdog or reset message
(see MO command).

D A Digital and Analog Control

D O Default Operating Parameters

Turn analog customization on *01WE

Inquiry *01AN

Write string A *00WE

Inquiry *00A=

Set parameters *99WE

(no parity, 1200 baud) *99BP=N1200

Write string B *00WE

Inquiry *00B=

Inquiry *00CK

Write string C *00WE

Inquiry *00C=

Turn on analog output only *00DA=A

Inquiry *00DA

Set DO parameters *00WE

(factory default setting) *00DO=E

Example
Input (1)

*01AN=ON

*00A=2-8-95

*00B=123.4567

*00C=This_is_

*00WE

Inquiry *00DO

D S Deadband and Sensitivity Control

(set deadband to 20 x 0.005% = 0.10%FS ) *00DS=20

Set DS parameters *00WE

Inquiry *00DS

D U Display Units Control

Set DU parameters *00WE

(set units to in. Hg) *00DU=INHG

Inquiry *00DU

D = Data String D

(up to 8 characters, a <cr> indicates end-of-message,Write string D *00WE
and more than 8 characters will not write to location) *00D=A_PPT!!!
The C and D string can be used for a watchdog or reset message
(see MO command).

F = Custom Full Scale Range

Set F= parameter *00WE

(set custom FS range to 10.5psi) *00F=10.5

Inquiry *00D=

Inquiry *00F=

H = Highest Analog Output Voltage

(set analog high value to 82% x 5V = 4.2V) *00H=82

Set H parameter *00WE

Inquiry *00H=

Note: See Section 5.10 for complete command descriptions.

9

Example
Response (2)

#01AN=ON

?01A=2-8-95

?01B=123.4567

?01CK=OK

?01C=This_is_

?01DA=A

?01DO=E0N

?01DS=00S0

?01DU=INHG

?01D=A_PPT!!!

?01F=10.500

?01H=82

I C Idle Count Parameter

(set idle count to 12 , so that 12 output samples are skipped) *00IC=12

Set IC parameter *00WE

Inquiry *00IC

I D Identification Number

(set device ID of first null addressed unit to 12) *00ID=12

[RS-232] (set group ID of unit 12 to 95) *12ID=95

[RS-232] Group no. inquiry of device ID=12 *12ID

[RS-485](set group ID of unit 12 to 95 with group sub-address of 01) *12ID=9501

[RS-485] Group no. inquiry of device ID=12 *12ID

I N Initialize PPT Microprocessor

Stop all current operations *99IN

(does not affect RAM data)

Full reset of PPT processor *99IN=reset

Changes to RAM data are lost unless an SP =ALL command

was previously issued. (Response is user message, if selected) ?01Pressure_tank_1

I = Integration time

(set output rate to 50 readings/second) *00I=R50

L = Lowest Analog Output Voltage

(set analog low value to 28% x 5V = 1.4V) *00L=28

Set ID number *00WE

Confirmation of ID=12 *12P1

Set group number *12WE

Set I parameter *00WE

Inquiry *00I=

Set L parameter *00WE

Inquiry *00L=

M = Maximum Full Scale Value Allowed

(Factory set) Inquiry *00M=

M O Power Up Mode

Set MO parameter *00WE

Required to save in EEPROM for power-up *00SP=ALL

Inquiry *00MO

N E Digital Input Enable to Analog (DAC) Output

Set a DAC analog output voltage *00NE

(example to set output of DAC to 2.5Volts) *00N=2500

Set continuous PPT DAC parameters *01NE=DAC

(set the PPT#01 DAC output to 2.5Volts) *01N=2500

(set the PPT#01 DAC output to 1.25Volts) *01N=1250

(set the PPT#01 DAC output to 0.1Volts) *01N=100

N = Send Number To DAC

(set analog output value to 4096mV = 4.096V) *00N=4096

Set N= parameter *00NE

See also the H=, L=, O=, and W= commands to control the analog output

O= Offset Pressure Window For Analog Output

Set O= parameter *00WE

(set pressure offset window to 28% x 20 psi (FS) = 15.6 psi) *00O=28

Inquiry *00N=

Inquiry *00O=

Example
Input (1)

*00MO=M1
*00WE

Example

Example
Response (2)

?01IC=12

#12CP= 14.32

#12ID=95

#12ID=9501

?01I=R050

?01L=28

?01M=0010psid

?01MO=X2M1

?00N=4096.0

?01O=28
Example

Note: See Section 5.10 for complete command descriptions.

1 0

O P Operating Mode Parameters

(set to extended binary output mode) *00OP=E

P1 Pressure, Single, ASCII Format

Request compensated pressure *00P1

P 2 Pressure, Continuous, ASCII Format

Request compensated pressure *00P2

P 3 Pressure, Single, Binary Format

Compensated pressure (null address) *00P3

Compensated pressure (assigned address) *01P3

(typical response is a ^ or { char plus 4 data bytes

that are encoded for computer translation)

P 4 Pressure, Continuous, Binary Format

Compensated pressure (null address) *00P4

Compensated pressure (assigned address) *01P4

(typical response is a ^ or { char plus 4 data bytes

that are encoded for computer translation)

P = Production Date

(factory set date, mm/dd/yy) Inquiry *00P=

R R Reading Rate

(skip 5 x 100 = 500 readings if identical) *00RR=5

RS Read Status

S2 Speed Shift to 2X

(shift to double speed if pressure changes *00S2=12

more than 12* 0.01%FS = 0.12% FS)

S5 Speed Shift at 50msec Intervals

(Output reading if pressure changes *00S5=60

more than 60 * 0.01%FS = 0.6% FS)

S I Synchronize Pressure Integration

SP Store Parameters in EEPROM

(store all settings stored in RAM in EEPROM) *00SP=ALL

S= Serial Number

T1 Temperature, Single, °C

T 2 Temperature, Continuous, °C

T 3 Temperature, Single, °F

Request Fahrenheit temperature *00T3

T 4 Temperature, Continuous, °F

Request Fahrenheit temperature *00T4

Note: See Section 5.10 for complete command descriptions.

Input (1)

Set OP parameter *00WE

Inquiry *00OP

Set RR parameter *00WE

Inquiry *00RR

Inquiry *00RS

Set S2 parameter *00WE

Inquiry *00S2

Set S5 parameter *00WE

Inquiry *00S5

Synchronize Integration *01SI

Store parameter *00WE

Inquiry *00S=

Request Celsius temperature *00T1

Request Celsius temperature *00T2

1 1

Response (2)

?01OP=ANEW

?01CP= 14.450

?01CP= 14.450
(repeated)

^@PSA or
{@PSA

^@P@@or

{@P@@

(repeated)

?01P=04/13/95

?01RR=5

?01RS=0000

?01S2=12

?01S5=60

?01S=00005137

?01CT= 24.5 or ?01CT= ..

?01CT= 24.5 (repeated)

?01FT= 76.1 or ?01FT= ..

?01FT= 76.1 (repeated)

T C Tare Control Switch

T O Transceiver Operating Parameters

Set RS485 response delay to 2 character times *01WE

T = Set Tare Value

(set tare to 10% of full scale; 10psi for a 100psi PPT) *00T=0.1

U = User Supplied Display Units

V = Version Number

W E Write Enable to EEPROM or RAM

Set tare value to current pressure reading *00WE

Set tare value to a % of full scale pressure *00WE

(example to set output units to cm water column) *01DU=CMWC

(Cancel continuous WE=RAM command) *01WE=OFF

Turn tare control on *00WE

Inquiry *00TC

Inquiry *01TO

Inquiry *00T=

Set display units *00WE

(set units to 5.1 x psi) *00U=5.100

Activate user display units *00WE

Inquiry *00U=

Inquiry *00V=

Write several RAM parameters *01WE=RAM

(factory default setting) *01DO=D

Example
Input (1)

*00TC=ON

*01TO=2

*00T=SET

*00DU=USER

Example
Response (2)

?01TC=ON

#01TO=M2CN

?01T=0.1000

?01U=5.1000

?01V=02.3B6S2V

Note: Any command changes in RAM will be lost when the PPT is powered down unless an SP command saves them to EEPROM.

W= Set Width of Analog Pressure Window

Set W= parameter *00WE

(set pressure window width to 40% x 20 psi (FS)= 8 psi) *00W=40

X=, Y= Slope - User Compensation Control

(set user slope control to 0.005% x 17 = 0.085%FS) *00X=17

Note: The input slope and offset control are for user supplied mx+b correction. The Y= is for negative slope for differential units.

Z= Offset - User Compensation Control

(set mx+b pressure offset to 20 x 0.005%FS = 0.1%FS) *00Z=20

(null adjust output at zero pressure) *00Z=CAL

~ Command Header for Binary DAC Values (Need to set DA=G, N, or R to receive, or O, S, or U to transmit)

(set analog set point) *00W=S

Inquiry *00W=

Set X= parameter *00WE

Inquiry *00X=

Set Z= parameter *00WE

Inquiry *00Z=

?01W=40

?01X=17

?01Z=20

Then enable single RAM write for DAC *00NE

(example to set output of DAC to 2.5Volts) ~@#16

See also the H=, L=, O=, and W= commands to control the analog output

(1) A carriage return, <cr>, should follow each input. If the PPT has an established address of 12, for instance, then begin the

command with *12.. instead of *00...

(2) The responses shown here begin with ?01.. and are for a null address PPT. That is, a PPT that has not yet established unit

identification (see ID command). If the PPT has an assigned address of 23, for instance, the response will begin with #23..
instead of ?01...

Note: See Section 5.10 for complete command descriptions.

1 2

4 FUNCTIONAL OPERATION

4.1 OVERVIEW

Honeywell’s Precision Pressure Transducer (PPT) is based on a silicon piezoresistive sensor coupled
with a microprocessor and other electronic circuitry. The piezoresistive sensor contains both pressure
sensitive and temperature sensitive elements which, when modeled over a matrix of pressures and
temperatures at the factory, provides a digitally compensated pressure reading. The PPT has a
typical accuracy of 0.05% of full scale (FS) and the PPTR has a typical accuracy of 0.10% FS over a

-40 to +85°C temperature range. This accuracy is achieved by compensation algorithms in the
microprocessor. Because of the internal digital circuitry, having a digital output capability is straight
forward. The digital readings are transmitted via RS-485 signals or RS-232 signals—which are
commonly available on most personal computers. When connected to a computer, the user can modify
the pressure reading rate, integration times, units of pressure, thresholds for deadbands and more.

In addition, a temperature compensated analog output is available. Analog output parameters can be
modified by the user when the PPT digital communications port is connected to a computer, or host
processor. For example, the factory set range of 0 to 5 VDC for the analog output voltage can be
modified to 1 to 5 VDC operation or any voltage span within the 0 to 5 volt range in 1% increments.
Those who choose to use the factory set defaults may use the analog output without ever connecting
to a computer.

The analog output is driven by a 12-bit digital-to-analog converter (DAC). Because the PPT has an
internal EEPROM (Electrically Erasable Programmable Read Only Memory) to store configuration
settings, it can replace conventional analog transducers without connecting to a serial bus. Program
your settings once and use it as a three-wire device—Power, Analog Out, Ground.

Pressure

Input

PPT

Pressure

Sensor

Temperature

Sensor

The PPT can be tailored to specific application requirements. Configuration information is sent to, or
read from, the PPT by user command messages over the serial port. Any configuration parameter
that can be changed by a command may be retrieved by use of that same command. Commands used
to change parameters must be preceded by an enabling command (WE or NE), but commands used
to retrieve information do not require an enable. All configuration changes are stored in the PPT
RAM for immediate use until power is removed. These configuration changes are only made perma­nent in the EEPROM when the user executes the Write Enable (WE) command followed by the
EEPROM Store Parameters (SP) command. Exceptions to this are the A=, B=, C=, and D= com­mands which are immediately stored to EEPROM if preceded by the WE command.

16 bit

Anaolg

to

Digital

Converter

Figure 4.1—PPT Block Diagram

EEPROM

Micro-

processor

1 3

RAM

Voltage Regulator

RS-232 or

RS-485

Driver

12 bit DAC

DC

Power

COM

(Digital

Serial
Data)

0-5V

Output

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 Sensitiv­ity (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 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.

1 4

r

r

g

DA = n

f

f

r

g

p

PPT supplied value

Output Control

Digital and

(DA=B factory default)

Computer or remote

Analog Control

IC = c

Idle Count

(IC=000 factory default)

if c = 0 then no output

if c = 1 - 255 then add 'c' wait

s

Speed Shift

S2 = s, S5 =

PPT Pressure Rate Conditionin

Dead Band and Sensitivity

DS = dd Sn

User Compensation

Integration Time

I = Rn or I =m MN

e

if s = 0 then disable

(S2=00 factory default)

(S5=00 factory default)

Dead Band

DB = n x dd x 0.005% FSrange

(DS=00S0 factory default)

ration

Inte

(I= M002 Factory default)

range for n value: 1-120

Shaded blocks represent command codes executed in the microprocessor

D - Digital onl y

others - see DA command

B - Both analog and digita l

n= A, B, D, N, O, R, S, T, U

A - Analog only

Select

Digital/Analog

Delay

I = Mn

i

I = Rn

i

cycles between inputs

Display Units

Scalar

.

Output Rate

Display Units and Tare

if s = 1 - 15 then th

threshold = s x 0.01% FS

S2 causes output rate to

double speed

S5 causes output changes

every 50 msec.

Tare Control

(gauge)

User Compensation

Press. = mX + b

(dd= 0 - 60, n=1, 2, 4, or 8)

(X=m+, Y=m, Z=b)

X=nn, Y=nn, Z=nn

(X=Y=1.000 factory default)

A/D

Converte

Rn: n readings/sec

Mn: n x 100 msec/reading

Pressure

Input

Figure 4.2—Pressure Reading Control

1 5

DAC

Output levels

Offset/Window

H=, L=

O=, W=

Pressure

Reading Rat e

Operating Mode

OP = d m n p

P1, P2, P3, P4

RR =

(RR=00 factory default)

(OP=ANEX factory default

Output

Analog

ut Control

Out

Output Mode

and Format

if d = A then output every input

if r = 0 then output every input

if d = U then output only changes

if p = X then no watchdog timer

Digital

TD, RD

Outputs

RS-232 or

RS-485

Driver

• ASCII, Binary, o

digitized analog

• Single or Continuou s

identical readings

if r = 1 - 10 then skip r x 100

if p = W then use watchdog timer For binary format mode

if m = N then no checksum

if m = C then use checksum

if n = S then use standard format

if n = E then use extended format

4.4 OUTPUT VOLTAGE CONTROL

A key feature of the PPT is the ability to configure the pressure range to a specific application by
issuing commands from a PC or host computer. All configuration changes can be stored in the PPT so
that it will power-up with those parameters set. This allows the user to set-and-forget any custom
configuration changes and use the PPT in the analog output mode from then on. The pressure range
and analog output parameters can be tailored to a specific application by using a simple set of PPT
commands. These commands (H=, L=, O=, and W=) are described below.

The output analog voltages for the zero reading and full scale reading are set at the factory to zero

and five volts. If the analog measuring device in the application has a low level input limit of 1 volt

and a high limit of 4.85V, the PPT can be configured to accommodate this. The lower limit can be set
to any value between 0 and 5 volts in 50 millivolt increments (1% FS steps). The AN=ON command
must be set. For example, the low output limit can be changed from 0 volt to 1 volt by using the
command *ddL=20 (20% x 5V = 1V). Similarly, the high output limit can be changed from 5 volt to

4.850 volt by using the command *ddH=97 (97% x 5V = 4.85V). Figure 4.3 shows the factory-set
output levels and Figure 4.4 shows the user modified output levels configured from 1V to 4.85V
range for a 20 psia unit.

Analog Out (V)

5

0

0

Pressure (psi)

The AN command has two options for reverse scale output: AN=ON- and AN=OFF-. When either
option is selected, the lowest pressure will output the highest analog voltage (H=) and the highest
pressure to output the lowest analog voltage (L=). Notice that the input pressure vs. output voltage
curves in Fig. 4.3 look similar. But note that the pressure values along the pressure axis have been
reversed. The curve on the right is how the analog range operates in the AN=ON- or AN=OFF-
modes. When visualized in this manner, the offset (O=) command works similar for both curves.
That is, the offset value moves the window (W=) from the origin (O=0) to the upper right (O=99).

AN=ON
AN=OFF

Figure 4.3—Factory Set Output Levels

20

Analog Out (V)

5

0

20

AN=ON ­AN=OFF -

Pressure (psi)

0

4.5 PRESSURE WINDOW CONTROL

The pressure range, or span and offset, can be user customized to accommodate a specific applica­tion. The user can scale the PPT’s pressure range over a smaller full scale span using the W= com­mand. Compressing the pressure range this way increases the output resolution per change in
pressure. The pressure range can be offset from the minimum pressure value by using the O=
command. These commands can effectively increase the analog output resolution by spreading it
over a smaller pressure range than full scale.

The O= command offsets the pressure window to reassign the minimum pressure value for the
lowest analog output. This command sets a pressure offset value from 0 to 99% of full scale. The

default is O=0%FS.

The W= command sets the width, or span, of the pressure window to a smaller range to fill the
analog output limits. This command sets a pressure window value, or span, from 0 to 99% of full
scale. A W=0 command will set the window to 100% and is the default value. For our example above,

1 6

a customized pressure span of 4 psi and offset of 12 psi can be configured from a 20 psia device by
using the offset (O=) and window (W=) commands. First, set the window offset to O=60 so that the

lowest analog output would begin at 12 psi (60% of 20 psi). Then, set the window width to W=20 so

that the pressure span is 4 psi (20% of 20 psi). The pressure range vs. output level curve is shown in
Figure 4.5.

4.85

Analog Out (V)

1

AN=ON

Pressure (psi)

Figure 4.4—User Modified

Output Levels

20

4.85

Analog Out (V)

1

Pressure (psi)

Figure 4.5—User Modified

Pressure Span

12

16

AN=ON

20

Using the store parameters command (SP), the configuration changes can be saved in EEPROM
so that the PPT will power up in that state ready to operate. This is particularly useful for
applications that use the analog output signal. The PPT can be configured and stored in the lab
and used in the field as an analog only instrument.

4.6 CUSTOMIZED PRESSURE RANGE

The user can adjust the pressure vs. output value transfer curve using the X=, Y=, Z= and F=
commands. The X= command adjusts the slope of the pressure output curve for positive pressures.
This applies to all absolute and gauge devices and modifies the positive full scale slope of PPTs. The
Y= command adjusts the negative full scale slope of differential PPTs. The Z= command adjusts the
offset of the pressure output curve. The range of adjustment for X=, Y= and Z= commands is
±0.6%FS in 0.005% increments. The F= command can change the full scale pressure span to any
value between 50% and 100% of the factory specified range (M=).

The purpose of these commands is to allow the user to provide compensation for the pressure values
specific to an application. This type of adjustment is made after the PPT temperature compensates

the pressure reading according to the factory calibration. The user supplied values (X=, Y=, Z=) are
used as an mx+b correction. The X= and Y= command supplies the slope adjustment, or ‘m’, value
and the Z= command supplies the offset adjustment, or ‘b’, value. Figures 4.6 and 4.7 illustrate these
commands.

Analog Out (V)

5

Figure 4.6—Custom Slope (X=) Options

+0.6%FS Slope=1

-0.6%FS

20 Pressure (psi)

Analog Out (V)

5

+0.6%FS

Figure 4.7—Custom Offset (Z=) Options

1 7

Offset=0

-0.6%FS

20 Pressure (psi)

The user compensated pressure output can be expressed in terms of X= and Y= slope values ‘m’
where m=0 to ±120. The offset value, Z=, can be expressed as ‘b’ where b=0 to ±120.

Pressure Output = [(1 + m x 0.00005) x Pressure Reading] + [(b x 0.00005) x (full scale)]

The F= command is used in conjunction with the X=, Y=, and Z= command to customize the full
scale range and user compensation of the PPT. The F= command allows the user to reduce the full
scale range of the PPT as much as one-half the factory FS value. The F= command value can have up
to 5 significant digits with a decimal point. Enter an F=0 command to disable this function and
return to the factory default (M=) full scale value. Using the F= command, the maximum allowable
full scale pressure is the M= value and the minimum allowable FS pressure is (0.5 x the M= value).
The new F= value becomes the standard FS number used for other commands and range calcula­tions. Note that the accuracy specification is always referenced to the factory (M=) full scale value.

For example, to customize the full scale range of a 20 psig (554 in. water column—inwc) device to 300
inwc, first select the desired display units using the DU command. Enter the command *ddWE
followed by a *ddDU=INWC. Then enter a *ddWE followed by a *ddF=300. The full scale pressure
for this unit is now 300 inwc.

4.7 SETTING ANALOG PRESSURE SET POINT

Another feature of the PPT is the ability to program an analog pressure set point that triggers the
analog output from the low voltage setting (L=) to the high voltage setting (H=) using the W= and O=

commands. These outputs can be used to activate alarms or lights based on pressure conditions. This
feature can operate in an analog only mode once the set point has been configured and stored to
EEPROM. The set point can be changed in the application through the digital RS-232 connection.

Analog Out (V)

5

12

20

Pressure (psi)

Analog Out (V)

5

Dead Band

12

20

Pressure (psi)

Figure 4.8—Pressure Set Point Set Figure 4.9—Deadband on Set Point

If a set point from a 20 psig unit was desired whenever the pressure equals, or exceeds 12 psi, then set
O=60 (12 psi = 60% of 20 psi FS) and W=S (for setpoint). Figure 4.8 illustrates the pressure vs. voltage

response curve. The output will change to 5 volts at 12 psi. The output levels can be changed by using
the L= and H= commands. If the unit was a 20 psid (differential), then the commands O=80 (32 psi =
80% of 40 psi FS) and W=S are used. The difference is that the offset (O=) is referenced to the mini­mum pressure value, which is -20 psi for the differential unit. If the pressure signal has some noise in
it, then a deadband should be added to the set point. For a 20psig unit, setting DS=60 will put a ±0.06
psi deadband around the 12 psi set point. That is, the output will switch from 0 to 5V at 12.06 psi for
increasing pressures and switch from 5 to 0V at 11.94 psi for decreasing pressures. The I= command
can be used to filter, by increasing the integration time, any noise on the pressure signal.

1 8

4.8 PPT ANALOG OUTPUT CONFIGURATIONS

The PPT is truly a smart sensor device, but it can also be used to replace conventional analog pres­sure sensors straight from the box. A benefit of using the PPT in the analog mode is that there is no

need for offset or span adjustments to achieve the specified accuracy across a -40 to 85°C (-40 to
185°F) temperature range.

When you receive a PPT, it is ready to output a calibrated analog voltage when power and a pressure
line are connected. For example, a 20 psi (pounds per square inch) unit straight from the factory will
have the characteristics shown in Figure 4.3. The voltage can be measured using a digital voltmeter
(DVM) or an analog meter—see Figure 4.10.

Pressure

Input

20PSIG

Analog Out

Figure 4.10—PPT Pressure to Analog Voltage

The PPT can be configured to transmit pressure in the digital mode and receive analog values, for
the DAC output, to drive a voltage independent of pressure (see Figure 4.11). When operating in this

mode (DA=R, G or N), the PPT will continue to provide calibrated pressure readings through the
digital serial bus. In addition, the control processor can control the analog output voltage from the
PPT independent of the pressure readings. This capability allows a single PPT unit to operate in a
closed loop mode for systems requiring valve control.

In

Out

PPT

Figure 4.11—PPT Pressure Readings and Analog Voltage Control

Two PPTs can be used to sense pressure at one location and drive the analog pressure output at a
remote location without a host processor. For example, a strip chart recorder or other analog input

device, is being used to monitor a pressure point in a remote location. If the analog signal is run
between locations, it will be subjected to electrical noise, line interference and connector electrical
losses. The pressure signal would require shielding, single point ground connections and line filter­ing. A solution to eliminate the effects of line losses and noise sources would be to transmit the
pressure information digitally to the strip chart recorder using two PPTs (see Figure 4.12).

Pressure

Input

PPT1

A (or GD)
B (or TD)

RS-485 (or RS-232)

(long distance)

Figure 4.12—Sensing Remote Analog Pressure

DC Supply

Analog Out

A (or GD)
B (or RD)

Common (GD)

4 2 1 3 8

- + - +

PPT2

1 9

+5.5 to 30V

DVM

V

s

RS-232
Pressure readings
Valve control

Signal Gnd

Analog Out

This can easily be accomplished using two PPT units, one at the pressure point and one by the chart
recorder. A two-wire digital interface would transmit PPT1 pressure information to the PPT2 re­corder point. The digital RS-232, or RS-485, line is more tolerant of noisy environments and connec­tor losses than an anaolg signal. Commercially available RS-232, or RS-485, drivers and repeaters
are available to extend the distance between the two PPT units, up to several miles if necessary. The
PPT2 unit can be placed close to the chart recorder with very little, if any, noise on the analog
output. When the RS-232, or RS-485, baud rate is set to 28,800 baud, the reading delay imposed by
the digital transmission is 2 msec. The benefit of using two PPTs this way is that it is quick and easy
to implement and that no software development is required. Using this technique, the RS-232
connections can be configured as a single two-wire bus that accommodates up to nine pairs of PPT
units simultaneously sensing remote pressures. In order to avoid bus collisions on a RS-485 bus only
one pair of PPTs may be operated in this mode.

The PPT units should be configured as follows so that they will begin transmitting and outputting
analog readings when power is applied (see Table 4.1). To connect additional PPT pairs to the RS-232
bus, configure each pair with a unique group number. Nine groups are available from number 90
through 98. The example shown in Table 4.1 assumes both PPT units are in the same group - factory
default group is 90.

Commands to setup PPT1

Commands to setup PPT2

Input Comment Input Comment
*01WE=RAM Write enable *02WE Write enable
*01DA=U Pressure to ‘~’ format *02DA=R Digital to analog output
*01MO=P4 Power up mode *02NE=DAC Enable write to DAC
*01WE Enable EEPROM write *02WE Enable EEPROM write
*01SP=ALL Store all to EEPROM *02SP=ALL Store all to EEPROM

Table 4.1—PPT to PPT Remote Sensing Setup Commands

4.9 COMMAND ILLUSTRATIONS

The figures below illustrate the commands that affect the pressure output rate. Figure 4.13 shows a
varying pressure signal having a reading integration time of 200 msec. If the small variations on the
pressure signal are considered noise and are undesirable, increase the integration time to time­average the pressure signal, and filter out the noise.

5.24

5.20

5.16

5.12

5.08

5.04

5.00

4.96

4.92

Pressure

(psi)

1.
0

Figure 4.13—Integration (I=) Command, Example 1

Integration Time (0.2 sec)

Integration Time = 0.2 sec

(I=M2 sets 2x100 msec/sample)

I = M2 IC = 0
S2 = 0 S5 = 0

RR = 0 OP=A

Integration time
PPT pressure output
Actual pressure

2. 3.
0 0

Time (sec)

2 0

Figure 4.14 shows the same pressure signal with a 1 second integration time reducing the noise varia­tions on the output readings. Of course, the penalty for doing this is reducing the response time to rapidly
changing pressures that are not considered noise.

5.24

5.20

5.16

5.12

5.08

5.04

5.00

4.96

4.92

Pressure

(psi)

1.
0

Integration Time (1 sec)

Integration Time = 1 sec

(I=R1 sets 1 reading/sec)

2. 3.
0 0

Time (sec)

I =R1 IC = 0
S2 = 0 S5 = 0

RR = 0 OP=A

Integration time
PPT pressure output
Actual pressure

Figure 4.14—Integration (I=) Command, Example 2

Figures 4.15 and 4.16 illustrate rapid pressure changes using the S2 and S5 commands. The Speed Shift
commands (S2, S5) allow the tracking of rapid changes while sampling less often when pressures are
slowly changing. A threshold is set independently for the S2 and S5 commands that tell the PPT when to
begin outputting samples at the higher rate. The S2 command causes the output rate to double. The S5
command causes the readings to be output at 50 msec intervals synchronous with the normal reading
rates.

Pressure

10.00

9.00

8.00

7.00

6.00

5.00

4.00

3.00

2.00

(psi)

S2 Threshold

(±0.15 psi)

x1

1.
0

Speed Shift S2=15 sets the threshold for x2 output rate
change as 15 x 0.01% FS = 0.15%FS. For a 100psi device,

this equals a ±0.15 psi pressure change.

Speed Shift - S2

x2 x1

3.0 5

.0

I = M5 DO=S
S2 = 15 S5 = 0
IC = 0 RR = 0
OP=A

x2

Time (sec)

PPT pressure output
Actual pressure

Figure 4.15—S2 Speed Shift Command Example

2 1