• Dwell time selectable from 100 ns to 1,300 seconds per channel
• Number of channels per scan selectable from 4 to 65,536
• Accepts counting rates up to 150 MHz at the fast analog input
• 1-MHz single-channel analyzer input with computer controlled upper- and lower-level discriminators independently adjustable from 0 to +10 V
• Computer adjustable discriminator thresholds on the fast analog input and the external channel advance input
• Zero dead time between channels: absolutely no lost counts and no double counting at channel boundaries
• No end-of-pass dead time
• Sum mode for signal averaging; Replace mode for single-scan data; Replace then Sum mode circumvents reset dead time between acquisitions
• Up to 1,073,741,823 counts per channel in single or multiple passes
• Automatic termination of data acquisition after a preset number of passes (up to 4 billion)
• The start of the scan can trigger the experiment, or the experiment can trigger the start of the scan
• Includes a ramp output with computer-adjustable sawtooth and triangular waveforms
• Complete with operating, display and analysis software
• All functions are computer-controlled
• SCA Sweep mode for recording pulse-height spectra and selecting accurate SCA windows
• Spectra and instrument settings can be saved on disk and recalled for further processing
• Software features include smooth, sum, strip, compare, and normalize spectra; peak-search, report, and user-defined job streams
• Horizontal scale calibration by least squares fitting to user-defined units
• A11 Programmer’s Toolkit available for ActiveX™ programming under LabVIEW®
, Visual Basic, or Visual C++
An Abundant Choice of Time Ranges
The EASY-MCS employs a crystal-controlled clock with 100-ppm accuracy and high-speed digital electronics to achieve a wide range of accurate operating parameters. With the dwell time per channel selectable from 100 ns to 1300 seconds, and a scan length variable from 4 to 65,536 channels, time scans ranging from 400 ns to 2.7 years can be selected.
No Dead Time Between Channels, and Zero End-of-Pass Dead Time
EASY-MCS employs sophisticated digital circuits to eliminate the dead time between channels that is typically encountered in lower-performance multi-channel scalers. The result is absolutely no loss of counts and no double counting as the multichannel scaler advances from one time channel to the next. Fast digital processing also ensures that there is no end-of-pass dead time before starting a new scan.
Versatile Counting Inputs
Two different types of counting inputs make the EASY-MCS adaptable to virtually any source of signals. The fast analog signal input (IN) accommodates both analog and digital signals with pulse widths >3.5 ns and counting rates up to 150 MHz. The input discriminator threshold is computer adjustable from –1.6 V to +3 V in steps of 1.5 mV (pulse must be >30 mV amplitude). This facilitates the preferential selection of larger pulses for counting, and the rejection of noise. Triggering can be selected for either positive or negative slope to match pulses of either polarity.
For counting rates up to 1 MHz with positive analog signals, EASY-MCS offers the pulse-amplitude selectivity of the SCA input. This "Single-Channel-Analyzer" input features two computer-controlled discriminators, whose thresholds can be set anywhere between 0 and +10 V with 12-bit resolution. EASY-MCS counts only the analog pulses that rise above the lower-level threshold without exceeding the upper-level threshold. This input is ideal for analog signals whose amplitudes are proportional to a measurement parameter, such as the number of photons in a pulse. Pulse widths from 0.5 to 100 µs can be readily accommodated.
The Power of the SCA Sweep Mode
The SCA Sweep mode makes the setting of the SCA thresholds quick, easy, and accurate. In this mode the window width between the lower and upper SCA thresholds is held constant (at 1/512 of 10 V) while the computer repeatedly sweeps the position of the window from 0 to +10 V in 512 equal steps. In synchronism, the multichannel scaler repeatedly scans from channel 0 to 511, while counting the SCA output. The result is a display of the pulse-amplitude spectrum present at the SCA input. The mouse can be used to mark the lower and upper limits of a spectral feature in this display for selective counting in a subsequent multichannel scaler mode. Once these limits are marked, clicking the mouse on the "Set SCA" button in the display locks the lower and upper thresholds of the SCA into the exact settings that bracket the feature.
Improved Precision by Signal Averaging
For any selected dwell time and memory length, the data collected in each scan can either replace the data stored in memory, or can be added to the data in memory. The latter mode is useful for reducing statistical scatter. Effectively, it improves the signal-to-noise ratio by signal averaging. For random noise (noise that is not correlated with the Start trigger or the dwell-time clock), the signal-to-noise ratio improves in proportion to the square root of the number of scans added together. Selection of a "Preset Pass Count" programs the instrument to collect data for the desired number of scans (or passes), and then automatically stops data acquisition. Once data acquisition commences, the computer is free to run other software programs. To permit repetitive data addition to high precision, the preset pass count can be set to any value from 1 to 4,294,967,295, with a memory capacity of 1,073,741,823 counts per channel.
Versatile Scan Synchronization
EASY-MCS offers two methods for synchronizing the scans with the start of the events to be counted. Either the start of a scan in the EASY-MCS can provide the trigger for the events (internal trigger mode), or an external trigger for the events can start the scan (external trigger mode).
Internal Trigger Mode
The Start Output is a 160-ns wide, positive TTL signal, produced in synchronization with the start of a scan. This output can be used to trigger the external events. For example, this signal can trigger a LASER, whose output light pulse is used to excite phosphorescence in a sample. The decaying counting rate of photons emitted by the sample after each LASER pulse is counted by the EASY-MCS.
For measurements requiring analog control of a parameter (e.g., Mössbauer experiments), EASY-MCS provides a Ramp Output voltage proportional to the channel number in the scan. The ramp can be operated with either a sawtooth pattern or a triangular waveform. In the sawtooth mode, the ramp voltage varies linearly from the beginning voltage to the ending voltage as the scan progresses. At the end of the scan the voltage abruptly changes back to the beginning voltage. With the triangular pattern, the ramp voltage changes linearly from the beginning voltage to the mid-point voltage during the first half of the scan. During the second half of the scan, it makes another linear transition from the mid-point voltage to the ending voltage. All three voltages (Begin, Mid, and End) are adjustable via the computer from 0 to +10 V in 65,536 steps. For precise repeatability, the ramp profile is stored as a digital image in half the memory. This limits the memory length available for counting events to 32,768 channels when the ramp is active.
External Trigger Mode
In the external trigger mode, a positive TTL logic pulse delivered to the Start Input will initiate the scan in the EASY-MCS. The scan can proceed based on the internal dwell-time clock in the EASY-MCS, or the channel advance can be implemented by supplying pulses to the Channel Advance Input.
Using the internal dwell time, the scan starts on the first edge of the internal 50-MHz clock following the rising edge of the Start Input pulse. When the external channel advance is used, the scan starts as the rising edge of the first channel advance input pulse crosses its discriminator threshold, subsequent to the rising edge of the Start Input. The external channel advance input includes a computer-controlled discriminator threshold selectable from –1.6 V to +3 V in 1.5-mV steps (pulse must be >30 mV amplitude). This discriminator permits adaptation to a variety of signal sources at the external channel advance input. The minimum interval between external channel advance pulses is 100 ns.
Instrument Control at the Click of a Mouse
The EASY-MCS software operating under Windows‚ provides a powerful graphical user interface for spectral data display and for control of the instrument. All controls can be instantaneously activated on the computer display via the mouse. The most commonly used controls are always displayed alongside the spectrum. The less frequently used set-up parameters are easily accessed from drop-down menus. In addition to the quick action offered by the mouse, most controls can also be activated by keystrokes. For protection against power outages, all control settings are automatically stored on disk when the scan is started. In addition, settings can be saved in disk files, so that specific operating conditions can be recalled for later use.
Quick Access to Multiple Spectra
An on-screen control allows the operator to view either the spectrum being acquired in the EASY-MCS dual-port memory, or a spectrum previously transferred to the buffer memory in the computer. The full power to display and manipulate can be applied to the spectra in either of these memories. Spectra can also be saved as disk files for recall and examination later, or for further processing.
Full and Expanded Displays Reveal Quantitative Details
Two views of the selected spectrum are displayed. The box in the upper, right-hand corner always shows the full spectrum. A region selected and marked on this small display is expanded in the larger display for better resolution of details. By using the mouse pointer, a marker can be moved through the spectrum to a feature of interest. Simultaneously, the computer displays the horizontal coordinate for the channel designated by the marker position, and the number of counts recorded in that channel. By default, the horizontal coordinate is displayed as the channel number in the external dwell-time mode. In the internal dwell-time mode, the default horizontal coordinate corresponds to the selected dwell time. The horizontal scale can be easily calibrated in user-defined units through least squares fitting to a linear, quadratic, or cubic function. In that case, the marker position reads out in the calibrated units. Once calibration is accomplished, the operator can quickly toggle back and forth between the default and calibrated units.
The marker also serves to paint a "Region Of Interest" (ROI) on the spectrum. Typically, this is a colored region that marks the entire area under a peak in the spectrum. Single or multiple ROIs can be marked in a spectrum. Using the Data Info command under the Calculate menu, the marker can be positioned within an ROI to trigger the computer to display the centroid of the ROI, the gross (total) counts in the ROI, and the net counts above background in the peak.
More Options for Analysis
Further software features allow the operator to compare two spectra, subtract or add two spectra, normalize the vertical scale, subtract a flat background, or smooth statistical fluctuations. Also available is a routine that automatically finds each peak in a spectrum and marks it with an ROI. The centroids, gross counts, and net counts from all the ROIs in a spectrum can be printed, either with or without library matching. If the computer has been asked for a match to a user-defined library of peak locations, the library information will be printed along with the matching ROI data. In addition to the standard .MCS file format, spectra can be imported and exported as ASCII text.
Programmed Data Acquisition
Some measurements require changes in the data acquisition conditions as different spectra are acquired. The Start Job command under the Services menu provides an easy way for the operator to define a stream of Job Commands that varies the instrument settings and controls acquisition of multiple spectra. The Job Stream can be simple or sophisticated. Once the Job Stream is defined and implemented, data acquisition proceeds automatically under the Job Control.
Other software programs can activate the EASY-MCS for a specific operation by calling the EASY-MCS software with a Job file name specified on the command line. Alternatively, the A11 CONNECTIONS Programmer’s Toolkit can be purchased and used to program the EASY-MCS at the command level. The use of ActiveX™ Controls in A11 makes programming orders-of-magnitude easier with LabVIEW®
, Visual Basic, or Visual C++.