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dataTaker Networks

Up to 31 dataTaker 500/600 series loggers can be configured into a network via their NETWORK interfaces. The individual loggers in the network are supervised from a host computer connected to the RS232 COMMS interface of any of the loggers in the network. There is no slave / master hierarchy.

Host Computer Software

DeLogger 4 or DeLogger Pro 4 do not support the dataTaker network.

A dataTaker network can be supervised from DeTransfer, using the network addressing and commands described below.

Similarly, purpose written software can supervise a network using the network addressing and commands described below.

ThedataTaker Address

The individual dataTaker 500/600 series loggers in the network are identified by a unique address. This address is used

to direct commands to loggers on the network

to direct messages to the RS232 COMMS interface of loggers on the network

The dataTaker network address is prefixed to commands for particular loggers on the network.

The dataTaker 50 does not have a network interface. However the dataTaker 50 supports the address, and it is useful for identifying the logger in STATUS and STATUS1 commands, and for returning data prefixed with a logger address or number that identifies the source of data. The logger address is prefixed to returned data by enabling the Logger Address Switch (/L).

Setting the Address

The address of each of the dataTaker data loggers in a network is set by the 8 bit DIP switch which is located under the top cover of the logger. The logger network address can be set in the range 0 to 31.

When the top cover of the logger has been removed, the DIP switch can be found immediately behind the memory card socket. Bits 4, 5, 6, 7 and 8 of the DIP switch are used to set the address (See Section II ñ The NETWORK Interface).

Make sure that each logger in the network has a different address, otherwise conflicts will occur. The addresses do not need to be consecutive.

Directing Commands and Programs to Loggers

Commands and programs are directed to specific loggers in the dataTaker network by using the address of the target logger.

Directing Commands to the Local dataTaker

Whenever a command or program is to be sent to the logger in the network that the host computer is connected to, then no addressing is required.

BEGIN
 RA10M
   1V 2R 3F
END
LOGON

Commands without addresses are received and executed by the local dataTaker, and are not transmitted onto the network.

Directing Commands to the Remote dataTakers

When commands or programs are to be sent to a remote dataTaker data logger in a network, then the target logger must be identified by its unique address. The remote dataTaker address is prefixed to the command in the general format

#commands

where

#                       is the address identifier
n                       is the remote logger address (0 ñ 31)
commands           is the command or commands to be sent

Specifying the address of a remote logger in a command is illustrated in the following example

#4 STATUS

Specifying an address of a remote logger in a program is illustrated in the following example

#4 BEGIN
#4  RA10M
#4    1V 2R 3F
#4 END
#4 LOGON

In this case the local logger places the command or program onto the network, which is then identified and processed by dataTaker number 24 (if present).

The # character indicates that the following command is for the remote logger at the address specified.

Broadcast Address for Commands

A broadcast address for commands and programs is also supported by the dataTaker network. The broadcast address allows commands to be sent to the local logger, and to all remote loggers in a network. This is despite the fact that the individual loggers in the network are set to different addresses.

The broadcast address is prefixed to the command in the general format

##  commands

where

##                     is the broadcast address identifier
commands           is the broadcast command

Specifying the broadcast address for a command that is to be sent to all loggers in a network is illustrated in the following example

## /m/e/n/u  P22=44  T=10:30:00  CLEAR

Broadcasting commands to a network may be used to configure all loggers, to set the real time clock of all loggers, to clear the data memory of all loggers, etc. by a single command from the host computer.

If a broadcasted command results in the remote loggers returning data via the network, then because of the nature of the network protocol the data will return to the host in a random order from the networked loggers.

Communicating Messages to Other Devices on the Network

The host computer can communicate via the network with devices such as computers, terminals, printers and displays that are connected to the RS232 COMMS interfaces of remote loggers (remember that the host computer is connected to the RS232 COMM interface of the local logger).

Text strings or messages can be sent from the host computer to these devices by the command

@n  message

where

@                      is the message address identifier
n                       is the remote logger address (0 ñ 31)
message              is the text string or message to be sent

The @ character indicates that the message is not a command for the remote logger at the address specified, but is a message for the device on the RS232 COMMS interface of the remote logger.

The address of the remote logger is prefixed to the text string or message as follows

@5 HELLO THERE^M^J

In this case the message "HELLO THERE CR/LF" is sent from the host computer via the local logger and network to a device connected to the RS232 COMMS interface of logger number 5.

Control characters are included in the message in the format ^M (CR), ^J (LF), ^[ (ESC), etc. Note that CR/LF is not automatically appended to the message, and must be specifically included if required.

Broadcast Address for Messages

A special message broadcast address is also supported by the network. The message broadcast address allows a common message to be sent devices connected to the RS232 COMMS interfaces of all remote loggers in a network. This is despite the fact that the individual loggers in the network are set to different address.

The broadcast or wild card address for a message is prefixed to the message in the general format

@@  message

where

@@                    is the message broadcast address identifier
message              is the broadcast message

Specifying the broadcast address for a message is illustrated in the following example

@@ HELLO THERE^M^J

In this case the text string "HELLO THERE CR/LF" is sent from the host computer via the local logger and network to the devices connected to the RS232 COMMS interfaces of all remote loggers.

Control characters are included in the message in the format ^M (CR), ^J (LF), ^[ (ESC), etc. Note that CR/LF is not automatically appended to the message, and must be specifically included if required.

Path for Returned Data

Any data resulting from commands that were sent to a networked logger is returned to the local logger via its network interface. The local logger then transmits this data from its RS232 COMMS interface to the host computer ( unless the data is redirected to an alternative address ñ see below).

Note :  The local logger in the network must also have a unique address. Although addressing of the commands is not necessary when commanding the local logger, its address is used to indicate to remote loggers where data resulting from remotely directed commands is to be returned for output to the host computer.

Redirecting Data to an Alternative Address

By default all data from a networked dataTaker is returned to the host computer via the RS232 COMM interface of the logger which issued the command(s) to the networked logger.

However data can be redirected to another logger in the network, and transmitted from the RS232 COMM interface of that logger. This redirection is controlled by the setting of Parameter21.

This has use where a networked dataTaker is programmed via one dataTaker in the network, and returns its data to a display terminal or printer connected to the RS232 COMM interface of another logger in the network. Setting Parameter 21 to the address of the second logger will redirect the data to that logger.

Specifying the address for data to be returned to

#4 BEGIN
#4  RA10M
#4    1V 2R 3F
#4 END
#4 LOGON

#4 P21=3

Assuming logger #4 received the command via logger #1, then in this example all data produced by the program will be directed to logger #3 rather than returned to logger #1.

Setting Parameter21 to its default (P21=128) will restore the returning of data to the logger which transmitted the command on the network.

Addressing Returned Data 

Data that is returned to the host computer from the local logger, and from the remote loggers, is not normally prefixed by the address of the sending logger.

However the source of the data returned to the host computer from a network can be identified by two methods

enabling the Logger Address Switch (/L) (See Section III ñ Switch Commands)

using the Text Channel $ (See Section III ñ Text Channel).

The return of the dataTaker address is determined by the Logger Address Switch as follows

/L            Enable return of logger address
/l             Disable return of logger address (Default)

The Logger Address Switch defaults to disabled (/l) when the dataTaker is initially powered up, hardware reset or executes a RESET command.

The effect of enabling the Logger Address Switch (/L) is illustrated in the following example

#4 /L
#4 BEGIN
#4  RA15S
#4   1..5TK
#4   1..3DS
#4 END

In this case the logger number will be prefixed to the data returned to the host.

Logger 4
1TK  105.88 Deg C
2TK  107.76 Deg C
3TK  100.34 Deg C
etc.

Use of the Text Channel $ is to identify the source of data is illustrated in the following example

#4 $="Logger 4 - Boiler House"
#4 BEGIN
#4  RA15S
#4   1..5TK
#4   1..3DS
#4 END

In this case the Text Channel contains identification of a particular logger, and is returned as part of the data from that logger as follows

Logger 4 - Boiler House
1TK  105.88 Deg C
2TK  107.76 Deg C
3TK  100.34 Deg C
etc.

Networking and Low Power Mode

When the dataTaker data logger enters the low power mode (asleep), it will not wake when network activity begins. To ensure proper network operation the loggers must be kept awake by either externally powering the loggers, or setting Parameter15=2 to prevent the logger entering the low power mode (See Section III ñ Parameter Commands).

The Wake terminals of all loggers in a network can be linked together, such that when one logger wakes then all loggers wake.

Programming a dataTaker over the Network

The major difference between operation of a single dataTaker and a network of dataTakers is that management of the returned data and alarms becomes more involved.

The best method for managing the network will depend on the goals

data logging

monitoring for alarm conditions

rapid real-time response

simplicity of programming

telemetry or modem connection

Don't underestimate the complexity of managing large volumes of data. Unloading data over a network link from a dataTaker which has a large memory card can take over an hour.

There are two broadly different methods for network management, part-time and real-time networks.

Part-Time Network

If the main task is data logging, and communications between the network and the host computer can be infrequent (hours, days or weeks), then it is reasonable to program and unload each logger in the network individually. This is the same as using a single logger, except that each logger must be addressed.

Real-Time Network

Where the emphasis is for rapid response or for tracking conditions, network speed becomes vital. There are many ways the network can be managed. However as a general rule more speed leads to greater complexity in host software:

1. Polling channels one at a time. This method is simple but is slow. Polling over a network can take approximately 2 seconds before requested data is received.

However since only one operation is undertaken at a time, there can be no confusion about the source of the data.

For example when polling a channel (assuming /n/u)

#3  2V

Will return data as follows

156.54

The polling speed can be as low as one channel every two seconds.

2. Polling data back from installed alarms one at a time using the ?n command (See Section III ñ Alarms). This is similar to the first method, but will be faster because the logger returns the last reading of the test channel rather than initiating a new sampling.

3. Polling data back from groups of channels using the Schedule Triggered by Poll (RX)

To poll groups of channels, the appropriate Schedule is first entered into each logger in the network as illustrated below

#2  RX 2V 3..4TT(FF1) /u/n/L

#3  RX  1..4DS  /u/n/L

The networked dataTakers are then polled by the Poll Trigger command as follows

#2  X

#3  X

and will return data similar to

For Logger #2

2:156.54 23.5 28.9

For Logger #3

3:0 1 1 0

This method retains most of the simplicity of method 1, but is faster by scanning up to 20 channels every two seconds.

4. Poll all alarms on a logger by the ?ALL  command (See Section III ñ Alarms). This is similar to the previous method but is faster at approximately 30 channels every two seconds.

5. Data can be synchronously returned from loggers in a network which have been programmed by Triggered Schedules RA, RB, RC and RD (See Section III ñ Triggered Schedules).

This is the most flexible method as it allows each logger full control of running schedules, but to work it requires that the host software use's more complicated data routing and time stamping techniques.

6. The use of the Fixed Format data mode (/H) is recommended for real-time networks.

Network Error Messages

Various warnings and error messages are returned to indicate that errors in network communications have occurred.

If the local dataTaker is unable to send any commands or messages to remote dataTakers because of network failure, then one or more network error messages (E38, E43, E44, E45) are returned to the host by the local logger. These error messages are detailed in Section III ñ Warnings and Error Messages.

However if a remote dataTaker is unable to return data to the host computer because of network failure, then the error cannot be reported since the link has failed. In this case the remote dataTaker records the occurrence of the error, which can be returned either by the Parameter9 command or as System Variable 6 (6SV). This can later be checked when the link is repaired.

For example the network errors logged by logger 15 can be read by the command

#15 P9

or

#15 6SV

to determine if any errors have occurred.

After reading the network error variable, the variable can be cleared by the command

#15 P9=0

Network errors can be logged with other data by including the system variable with other channels to be scanned in schedule lists. For example the command

#7 BEGIN
#7  RA10M
#7   1..5TT  10V  6SV
#7 END
#7 LOGON

will log the number of network errors with the channel data.

Alarms can also be raised as a function of network errors, to provide active indications that the network is failing or has failed.

For example the command

ALARM5(6SV>0)1WARN

will warn of network failures on a display panel.

Page Content


Home

Title and Waranty

Go to: Section 2 | Section 3

Section 1


Construction of the dataTaker 50

Construction of the dataTaker 500 600

Construction of the CEM

Getting Started

 

Section 2


Interfacing

Powering the dataTaker

Powering Sensors from the dataTaker

The Serial Interfaces

The RS232 COMMS Serial Interface

The NETWORK Interface

Analog Process

Connect Analog

Analog Chns

Measuring Low Level Voltages

Measuring High Level Voltages

Measuring Currents

Measuring 4-20mA Current Loops

Measuring Resistance

Measuring Frequency and Period

Measuring Analog Logic State

Measuring Temperature

Measuring Temperature with Thermocouples

Measuring Temperature with RTDs

Measuring Temperature with IC Temperature Sensors

Measuring Temperature with Thermistors

Measuring Bridges and Strain Gauges

Measuring Vibrating Wire Strain Gauges

The Digital Input Channels

Monitoring Digital State

The Low Speed Counters

The Phase Encoder Counter

The High Speed Counters

The Digital Output Channels

The Channel Expansion Module

Installing The Panel Mount Display

 

Section 3


Programming the dataTaker

Communication Protocols and Commands

Entering Commands and Programs

Format of Returned Data

Specifying Channels

The Analog Input Channels

The Digital Input Channels

The Counter Channels

The Digital Output Channels

The Real Time Clock

The Internal Channels

Channel Options

Schedules

Alarms

Scaling Data - Polynomials, Spans and Functions

CVs Calcs and Histogram

Logging Data to Memory

Programming from Memory Cards

STATUS RESET TEST

Switches and Parameters

Networking

Writing Programs

Keypad and Display

Error Mess Text

Appendix A - ASCII

Appendix B - ADC Timing