Sensotec DS User Manual

Dual Output Pressure Sensor

Model DS

User’s Manual

008-0627-00

Version 1.10

Table of Contents

Chapter 1 Introduction
Chapter 2 Command Summary
Chapter 3 Command Format
Chapter 4 System Commands
Chapter 5 Digital Output Commands
Chapter 6 Analog Output Commands
Chapter 7 Electrical Connections

1.1 Overview

The Model DS Pressure Sensor combines high performance with the versitility of
both analog and digital outputs. The high accuracy pressure readings are fully
temperature compensated across the entire operating temperature range of the
transducer. In addition the Model DS Pressure Sensor maintains a maximum
update rate of 2500 times a second for both digital and analog outputs.

The Model DS provides a configurable analog ouput of 0 to 5 VDC. In default
operation, the fully temperatrue compensated voltage output is proportional to
the pressure applied to the pressure port. Alternately the analog output may be
configured for independent control by the user through the digital interface.

The Model DS provides a digital output of either a RS-232 full duplex interface or
a RS-485 half duplex interface which allows for multi-unit operation. Each
transducer has an universal address for setup and an user defined address for
multidrop operation. In addtion to pressure readings, all operating parameters of
the transducer are accessible through the digital interface. For example, user
adjustment of span and offset are provided for each output independently
through the digital interface.

1. INTRODUCTION

The following chapters detail the features and operating parameters of Model DS
Pressure Sensor.

1.2 SPECIFICATIONS

Power Requirements: 15 - 28 VDC

50 mA typ.
75 mA peak (during RS-485 operation)

Pressure:

Accuracy:

Digital: ± 0.05% of F.S. typ.

± 0.10% of F.S. max.

Analog: ± 0.10% of F.S. typ.

± 0.20% of F.S. max.

Resolution:

Digital: 0.05% or 5 significant digits
Analog: 1.4 mV steps

Operating Temperature Range: -40 to 180 Degree F

Digital output: RS-485 Half Duplex, or RS-232 Full Duplex

Baud Rates: 1200, 2400, 4800, 9600, 19.2K,

38.4K, 57.6K, 115.2K
Data Framing: 1 start bit, 8 data bits, 1 stop bit
Parity: No parity
Addressing; User assigned

1 null address (address not assigned)

Bus operating mode: Response to a designated unit request

(Master/slave)
Pressure Units: Shipped as PSI, field selectable
Update Rate: 2500 updates per second, maximum
Mechanical Shock: TBD
Thermal Shock: TBD
Vibration: TBD
Long term stability: TBD
Media Compatibility: Exposed surfaces are 316L stainless steel

2. Command Summary

2.1 System Commands

Detailed descriptions of each system command is given in alaphabetical order in
Chapter 4.

Command
Code

DC Display Temperature (Centigrade) No sddd<CR>
DP Display User Defined String No xxxxxxxxxxxxxxxx<CR>
DR Display Errors No Err_x<CR>
DT Display Temperature (Fahrenheit) No sddd<CR>
FC Read Calibration Date No dd/dd/dd<CR>

FE Read Serial Number No dddddd<CR>

FR Restore Factory Default Settings Yes OK<CR>

FT Test Data Storage Checksum No OK<CR>

II Set Update Rate Yes OK<CR>
R4 Read Unit Address No dd<CR>
R5 Read Full Scale Range No sd.dddddEsdd<CR>

RM Read Mfg. Part Number No xxxxxxxxxxxx<CR>
RR Read Software Revision No ddd-dddd-dd d.dd<CR>

Description Write Enable

Required

Typical Response

SP Set User Defined String Yes OK<CR>
W1 Write Baud Rate Yes OK<CR>
W4 Write New Address Yes OK<CR>

WE Write Enable No OK<CR>

Typical Response Key: d - decimal digit s - sign indicator: “+” or “-”

x - any valid ASCII character <CR> - Carriage Return
All other characters and punctuation appear as is.

2.2 Digital Output Commands

Detailed descriptions of each digital output command is given in alaphabetical order in
Chapter 5.

Command
Code

D0 Display Digital Pressure Reading No sd.dddddEsdd<CR>

DB Display Digital Zero Adjustment No sd.dddddEsdd<CR>
DE Display Eng. Units Conversion Factor No sd.dddddEsdd<CR>

DM Display Digital Span Adjustment No sd.dddddEsdd<CR>

R6 Read Engineering Units Label No xxxx<CR>

SB Set Digital Zero Adjustment Yes OK<CR>
SE Set Eng. Units Conversion Factor Yes OK<CR>
SM Set Digital Span Adjustment Yes OK<CR>

W6 Write Engineering Units Label Yes OK<CR>

Typical Response Key: d - decimal digit s - sign indicator: “+” or “-”

Description Write Enable

Required

x - any valid ASCII character <CR> - Carriage Return
All other characters and punctuation appear as is.

Typical Response

2.3 Analog Output Commands

Detailed descriptions of each analog output command is given in alaphabetical order in
Chapter 6.

Command
Code

DA Display Analog Output Voltage No sd.ddd<CR>
RN Read Analog Output Offset No sd.dddddEsdd<CR>
RO Read Analog Output Scaling Factor No sd.dddddEsdd<CR>
SA Set Analog Output No OK<CR>
SS Select Analog Output Source Yes OK<CR>
SV Set Analog Output Default Value Yes OK<CR>

SY Read Analog Output Default Value No sd.dddddEsdd<CR>

WN Write Analog Output Offset Yes OK<CR>
WO Write Analog Output Scaling Factor Yes OK<CR>

Typical Response Key: d - decimal digit s - sign indicator: “+” or “-”

Description Write Enable

Required

x - any valid ASCII character <CR> - Carriage Return
All other characters and punctuation appear as is.

Typical Response

3.1 Serial Protocol

The Model DS pressure transducer uses either a half duplex RS-485 or a full
duplex RS-232 hardware interface for serial communications. All serial
communication is in ASCII format using 8 data bits, one start bit, one stop bit and
no parity bits. Baud rates of 1200, 2400, 4800, 9600, 19.2K, 38.4K, 57.6K and

115.2K are available. As shipped from the factory, the baud rate is set to 9600
baud, the default baud rate.

3.2 Command Format

Each command is a string of ASCII characters. The following represents the
general format of the transducer commands:

#aaccxx...xx<cr>
# The pound sign is the start of command character.

3. COMMAND FORMAT

aa This two byte field is the unit address.
cc This two byte field is the command.
xx...xx The data field is an optional field of up to 18 characters.
<cr> The carriage return is the end of command character.

3.2.1 Start of Command

The pound sign, ‘#’, ASCII code 35 decimal, indicates the start of a command.
The transducer continually monitors the serial communication bus, ignoring all
characters until the pound sign is detected. Once the pound sign is detected the
transducer enters receive mode and begins looking for a valid address.

3.2.2 Unit Address

The unit address is a two character field of ASCII alphanumeric characters. The
address may be any combination of numerals or letters and is case sensitive.

Each transducer supports two addresses. The first is an universal address to
which all transducers respond. The address of ‘ff', (ASCII codes 102 decimal,
102 decimal) is reserved as the universal address. This universal address should
not be used when multiple transducers are setup as a RS-485 network. All

transducers on the network will respond to this address at the same time
resulting in corrupted responses.

The second address is an unique, user defined address to which only the
specific transducer will respond. The user must define this unique address using
the W4 command. As shipped from the factory, the default value for this address
is ‘00" (ASCII codes 48 decimal, 48 decimal).

After the transducer detects the start of command character and enters receive
mode, it monitors the serial communications port for a valid address. If the
address found is the universal address or the transducer’s unique address, the
transducer will continue to process the serial communications for a command.

If the address found is not the universal address or the transducer’s unique
address, the transducer will exit receive mode and will return to monitor the serial
communication for a start of command character. If characters received after the
start of command character are not ASCII alphanumeric characters, the
transducer also exits receive mode.

3.2.3 Command

A command is comprised of two ASCII alphanumeric characters. Commands are
not case sensitive; either upper or lower case letters may be used. The following
chapters offer a detailed explanation of each command.

3.2.4 Data Field

The data field is an optional field of up to 16 ASCII characters. This field contains
the data for commands which write data to the transducer. Valid characters for
the data field include all alphanumerics, decimal point, plus sign, and minus sign.

3.2.5 End of Command

The carriage return, ASCII code 13 decimal, indicates the end of a command. If
a command requires no additional data, the end of command character follows
the two character command. If a command requires additional data, the end of
command character follows the data field.

The transducer does not process a command until it receives an end of
command character. If the transducer does not receive a end of command
character within approximately 5 seconds after receiving a start of command
character, the command is aborted.

3.3 Command Response

The digital transducer transmits only in response to a command which uses its
unique address (or the universal address of ‘ff'). The transducer itself never
initiates a transmission.

There are two basic types of responses. The transducer will transmit an ASCII
string in response to commands which request data. This ASCII string is
terminated by a carriage return. For commands which do not request data, the
transducer acknowledges the command with ‘OK’ followed by a carriage return.
Examples of the typical response for each command are included in the
following chapters.

NOTE: Commands which change the operating parameters of the transducer are
implemented immediately. Changes are written to nonvolatile memory with each
command issued. Nonvolatile memory is guaranteed for 20,000 writes. A
checksum command is available to test the integrity of the nonvolatile memory.

The transducer indicates the following error conditions:

Response Description
Err_NaC Not a Command: The command was not recognized as a

valid command by the transducer.

Err_AcD Access Denied: The required Write Enable command did

not preceed the present command.

Err_NaN Not a Number: The data accompanying the command do not

represent a valid number.

Err_InF Invalid Format: The data accompanying the command do

not represent a valid option for the command.

Err_CsF Checksum Error:This response to the FT command

indicates a checksum error in data storage.

Err_OvR Over Range: This response to the D0 command indicates

the input pressure is approximate 6 % above the full scale
range of the transducer.

Err_UnR Under Range: This response to the D0 command indicates

the input pressure is approximately 3 % below the range of
the transducer.

4. SYSTEM COMMANDS

4.1 DC Display Temperature (Centigrade)

DESCRIPTION

The DC command reads the temperature at the transducer’s sensing element.
This value is provided as a diagnostic tool. The accuracy of this value is not
guaranteed but is typically within ±2 degrees Centigrade.

The response to this command is a varible length string representing the
temperature in degrees Centigrade.

EXAMPLE

#00DC

This command, followed by a carriage return, returns the temperature in
Centigrade of the transducer with the address of ‘00'.

Typical responses to this command illustrating the varible length of the response
include:

43
8

-5

-14

4.2 DP Display User Defined String

DESCRIPTION

The DP command displays the character string set by the SP command. This
character string is 16 characters in length. The default value for this character
string is 16 blank spaces (ASCII code 32 decimal).

EXAMPLE

#00DP

This command, followed by a carriage return, reads the character string set by
the SP command from a transducer with the address of ‘00'.

The transducer transmits a response to this command similar to: