Many of the dataTaker commands relate to sampling or reading input channels, setting output channels, executing calculations, testing alarms, returning data, logging data, etc. These processes usually involve one or more channels, which must be specified to the process in various ways. This chapter describes this channel specification.

Usually these processes are associated with a Schedule, which determines when the processes are performed. Conversely Schedules can be thought of as having a list of processes to perform, which is called the ëschedule listí or sometimes ëchannel listí if it only includes input channels to be read.

The specification of channels includes the module number on which the channel is physically located, the channel number, the type of signal or sensor connected to the channel, and various channel management options.

Channel Module

The input and output channels are located either on the dataTaker data logger, or on one or more Channel Expansion Modules connected to the data logger (dataTaker 500/600 series loggers only).

The dataTaker is always module number of 0 (zero). The Channel Expansion Module(s) connected to the logger are allocated module numbers 1 and 2 respectively in the order of position relative to the logger. Module number 1 is nearest the dataTaker.

The module number for each Channel Expansion Module connected to the logger is allocated during power up, and whenever the dataTaker executes a RESET command.

If the position of Channel Expansion Modules in a daisy chain are changed, then the dataTaker must be repowered or reset to reallocate the module numbers.

The module number is specified as part of the channel identification in the format

module:channel

where

module         is the number of the module on which the channel is located
channel         is the channel number on the module

The module number of the dataTaker is optional, and does not need to be specified. If a module number is not specified, then the module number defaults to 0 for the dataTaker.

Therefore where a dataTaker has no Channel Expansion Modules connected, then the module number is not required as part of channel specifications.

The module number is returned with the data as part of the channel identification.

Channel Number

Channels are specified in the schedule list as individual channels, or as a continuous sequence of channels in the general format

first_channel[..last_channel]type(options)

where

first_channel      is the first channel number
..                    indicates a continuous sequence
last_channel      is the last channel number
type                is the signal type identifier
(options)           are channel management options

The ..last_channel is optional, and if this is omitted in a channel specification then the first_channel is interpreted as an individual channel of the type specified as follows

channeltype(options)

Throughout this manual a single channel is indicated by the general format

ntype(options)

and a continuous sequence or group of channels is indicated by the general format

n..mtype(options)

When channel number sequences are defined, there may be one or more periods between the first and last channel.

If the channel(s) are located on Channel Expansion Modules, then the general format for channel specification is as follows

module:ntype(options)
module:n..mtype(options)

where

module      is the module number, 0 for the dataTaker and 1 or 2
               for successive Channel Expansion Modules

Channel number sequences can only be defined within modules, and cannot cross module boundaries.

The dataTaker will return an error message if module numbers are specified for non-existent modules.

DeLogger also identifies channels to be measured by the channel number, which are displayed by holding down the right mouse button on the work area of the Program Builder

 

 

 

The number of channels displayed varies for the type of input, and for the type of data logger that DeLogger is connected to.

Signal Type Identifier

A signal or sensor type identifier is suffixed to the channel number or channel number sequence to further identify the channel.

The various signal type identifiers for the input and output channels of the dataTaker are detailed throughout Section II and Section III of this manual, and are summarised in the following chapters.

Some examples of channel specifications for the dataTaker module follow

3V          analog channel 3, voltage
8TK         analog channel 8, thermocouple type K
2DS         digital channel 2, state
3..5I       analog channels 1 through 5, current

Some examples of channel specifications for Channel Expansion Modules follow

0:2L            dataTaker analog channel 2, current loop
1:6PT385        CEM 1 analog channel 6, RTD type 385
2:2DSO          CEM 2 digital output channel 2

Schedule lists are simple groupings of individual channels into a list for scanning, etc. as the following example illustrates

In DeLogger, the types of signals or sensors that can be input to channels are selected descriptively from the hierarchical walking menus in the Program Builder.

 

 

When the required signal or sensor group is selected, a dialog opens which displays the connection options for that group, and other input fields appropriate to the group

 

 

 

Channel Management Options

All signal types can be modified in various ways by channel options, which define the way in which the input channel and attached sensor is managed when read.

These options include types of sensor excitation, termination of the signal, specifying internal or external referencing for analog signals, scaling of measured data, format and destination of channel data, delays for digital output switching, etc.

Each channel type has default channel options, which do not need to be specifically declared. The declaration of channel options is itself optional.

The various channel management options are discussed in detail in Section III ñ Channel Options, and relevant sections throughout this manual.