Keyboard and Display The 2537A is controlled by an embedded microprocessor, allowing a wide range of features to be implemented. Virtually all instrument interaction is through a 16 button keyboard and LCD display. The software is menu driven, allowing easy alteration of the various instrument parameters. The 4 line by 40 character liquid crystal display is used to display and alter all measurement parameters, as well as to show the current status of the instrument. A piezo-electric sounder provides audible keypad feedback and error warnings.
Analog Outputs Two 0 to 5 volt analog outputs can be programmed to output any of a number of instrument internal and final signals.
Serial Port A serial RS-232 port can provide a report line for each instrument measurement. This port can also output the results of calibration cycles as well as method parameters and internal settings. In most cases a dedicated printer or data capture microcomputer will be connected to this port. The output format can be readily imported into most popular spreadsheet or database programs.
Digital Outputs Six digital outputs are provided to signal the internal status of the instrument.
Control Inputs A rear panel connector provides status and control inputs that allow recording of up to three external events. External control over calibration functions is also provided.
Non-Volatile Memory The microprocessor includes non volatile memory that allows the analyser to retain the following information when power is removed.
- all instrument settings and parameters
- results of most recent calibration
- two complete user defined analytical methods
Sample Volume Measurement A precision mass flow meter (MFM) is used to measure sample flow rate through the cartridge. The microcomputer integrates flow rates over time to provide the total volume of air measured for each sample. The instrument is supplied with volumes referenced to Normal temperature and Pressure (NTP), however this can be easily changed if required.
The speed of the sample pump is controlled by a closed loop feedback controller to ensure that the flow rate is set to the sampling rate specified in the current operating method. Controlling the speed of the pump results in quieter, more energy efficient operation, as well as longer pump life.
Optimal Carrier Gas Utilization A programmable mass flow controller (MFC) allows the flow of carrier gas to be altered for optimum performance during the various steps of the desorption cycle. In addition to improving sensitivity and repeatability, this feature conserves carrier gas, greatly increasing the lifetime of a cylinder of Argon.
Cartridge Cleaning The instrument provides a mechanism whereby residual mercury is desorbed from the gold in a cartridge before it is used for analysis. This process is automatically performed on each cartridge before a calibration or a run begins. Regular cleaning, together with short cycle times and small cartridge loadings, virtually eliminates the "memory effect" previously associated with pure gold cartridges.
Fully Programmable Measurement Cycle The sampling time and sample flow rate, and all steps in the desorption cycle are fully programmable. Two complete "methods" (sets of cycle timings and flow set points) may be entered and retained by the instrument.
Injection and Permeation Source Calibration The instrument has provision for two methods of calibration: manual injection and, for analysers so equipped, a mercury vapour permeation source.
Permeation source calibrations may be initiated automatically at regular intervals, allowing long term unattended operation. It is also possible, at any time, to manually initiate a recalibration using the source.
