Model 9615 - ICB Programmable Spectroscopy Amplifier

Features

• Complete programmability within the Genie™ family
• Uses the CANBERRA Instrument Control Bus (ICB)
• Automatic fine tuning of critical parameters: Pole/Zero matching, BLR rate, BLR threshold, PUR threshold
• Gaussian/Triangular shaping
• Differential input
• Front panel common mode balance control
• Pileup rejector and live time corrector
• Secure computer operation without conflicting front panel controls

Description

The Model 9615 Amplifier represents the latest in a programmable spectroscopy amplifier design and includes all the features associated with a research grade signal processor. Part of CANBERRA’s Instrument Control Bus (ICB) line of programmable front end electronics, this Genie Controlled Amplifier features: differential inputs for common mode noise rejection, wide gain range, choice of semi-Gaussian or semi-Triangular pulse shaping to meet most detector applications and requirements, a flexible Baseline Restorer and an integral Pileup Rejector (PUR) and Live Time Corrector (LTC).

The Model 9615 features Automatic Fine Tuning (AFT), which combined with computer control, makes the unit easy to set up and use. Critical performance adjustments are automatically optimized, eliminating the subjectiveness and guesswork normally associated with manual fine tuning. The results are consistent and repeatable, and nearly operator independent.

With the Model 9615 there is no need for an oscilloscope to optimize pole/zero (P/Z) matching: the operator simply starts the optimization process from the computer. The P/Z BUSY LED lights and the matching circuit begins converging on the optimal setting required for good high count rate resolution, peak stability and overload recovery. When the process is complete, the P/Z BUSY LED turns off and the computer stores the latest P/Z setting.

The P/Z BUSY LED will blink and the computer will be signaled if convergence is not achieved within two minutes. When power is turned ON, the LED will blink until the computer loads the P/Z setting or initiates another convergence.

The PUR threshold is automatically set just above the system noise level, insuring PUR efficiency and minimal spectral distortion due to pile up at high count rates. The restoration rate and threshold are automatically fine tuned for all shapings, gain and count rate conditions.

The Model 9615 employs three active complex-pole filters for improved pulse symmetry, reduced pulse dwell time and high throughput. For additional flexibility, semi-Gaussian or semi-Triangular pulse shaping are selectable.

Triangular shaping offers superior energy resolution due to its inherently longer rise time, better signal to noise ratio and reduced sensitivity to detector rise time variations. The Amplifier offers six switch-selectable shaping time constants, which effectively doubles to 12 when the choice of Gaussian and Triangular are both considered, allowing optimum matching for most detector and count rate requirements. This switch is located on the rear panel of this dual-width NIM module to avoid any casual operator intervention. Although a manual adjustment, the setting is read your Genie software to insure proper operation.

The gated baseline restorer with automatic rate and threshold assures the best possible low and high count rate resolution performance. The flexibility of the baseline restorer is further enhanced with programmed Asymmetrical and Symmetrical restorer modes. The Asymmetrical mode virtually eliminates charge accumulation and correlated noise on the restorer holding capacitor and is especially suited for use with high resolution detector systems. The Symmetrical mode allows performance optimization for detector systems which exhibit baseline discontinuities resulting from excessive noise, microphonics, high voltage effects, and preamplifier secondary time constants.

The Model 9615 has a differential input stage which can be used to suppress noise caused by ground loops, laboratory environment EMI and the resultant noise pick-up on cables and so forth. It is especially useful for applications which require long cables between the detector/preamplifier and amplifier. As with most other CANBERRA amplifiers, cable transformers are included in the Model 9615 to suppress high frequency noise normally associated with personal computer and MCA raster-type displays. A Common Mode Balance (CMB) control is conveniently located on the front panel allowing common mode rejection optimization for the specific application.

The Live Time Corrector and Pileup Rejector circuit allows quantitative gamma analysis nearly independent of system count rate. Special circuitry interrogates for pile up and permits the ADC to convert only those detector signals resulting from single energy events. To compensate for rejected pulses and pulse processing times, the Model 9615 generates a system dead time which extends the collection time by the appropriate amount. The front panel ACCEPT/REJECT LED indicates pileup rejector status.

The Model 9615 accepts programming information over an 8-bit wide CANBERRA bus standard called the Instrument Control Bus (ICB). ICB NIMs connect to this bus via a host module such as the Model 556A Acquisition Interface Module (AIM) as part of a hierarchy of networked acquisition and control managed by a Genie Family computing platform.

Adjustments are made through the graphical user interface of the Genie software environments. Equivalent batch procedure commands are also available in the environments. All ICB NIM parameters are stored in the single data file structure of the Genie family, allowing verification of correct set up from one experiment to the next.

All ICB NIMs feature a characteristic READY LED to indicate operational status.