In general, a data logger is a comprehensive and highly advanced Data Logger Summary. It is made versatile and flexible, to render it suitable for widely varying applications, specific requirements being met simply by setting up a suitable program.
It can accommodate from 10 to 1000 analog signals, depending upon the capacity of the analog scanner selected. There may be three or four poles per unit (or a combination) and the signal conditioning options of the scanner may be used. A digital voltmeter is used as the system A/D cinverter. The logger programs the voltneter (range, mode, integration period) according to the requirements of the particular input channel. Generally, data loggers are designed to drive two output recorders completely independent of each other.
The basic assembly of data logger consists of main frames, front panel assembly, and power supply unit, with the following essential modules.
- Scanner controller
- Data exchange
- DVM interface
The optional modules, the need for which depends on the requirements of the system, include the following.
- Data buffer store
- Alarm store
- Additional programmers
The function of various modules are as follows.
It is an interface between the logger and the analog scanner. It selects the channels for examination and receives the program location address from the scanner.
All data transfer within the logger is made via this module. It ensures correct transmission of data throughout the system.
It Controls the Sequence of events within the logger by defining and producing commands for the modules.
This is used to set up the channel programs, so that the DVM functions, output functions and alarm limit can be arranged for individual channels or groups of channels.
The DVM functions (range, mode, integration periods, etc.) are selected by the program instruction and transmitted via the interface.
After the completion of a measurement, the interface receives the DVM measurement data, which is then supplied to other modules in the logger.
6.Data Buffer Store
Measurement data can be held in a buffer store. Use of the store enables the logger to scan at speeds higher than the operating speeds of the output recorders.
During an alarm scan, and with an alarm store fitted to the logger, a channel is recorded only when it goes into or comes out of alarm. Hence repeated recording of the channel in alarm are avoided.
It provides scale factors and linearisation laws which convert the DVM reading into engineering units.
In additions to these modules, the basic assembly also provides facilities of digital clock, off limit detector and a display unit. The digital clock has an output of days (up to 99), hours, minutes and seconds which may be recorded on the output devices. It can command the logger to make measurements at practically any time interval.
The off limit detector allows any measured values of any desired channel to be compared to preset upper and lower limit values. When a channel is found to be outside limits, the fact may be indicated on the output record, or an external signal may be given, or the logger may automatically go into a different routine. The limit values are set up on the program pin board.
There are three main areas in which the operator can control and program the logger.
- Front panel controls
- Programmer pin boards on which channels programs are defined
- Diode matrices and soldered wire links on modules by which output format and code are defined.