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Junior Physics Laboratory
Operation of NIM modules
These summaries of NIM module operation should help you set up the experiments. More information and complete specifications for the commercial equipment can be found in the manufacturers' manuals.
A. Analog devices Pre-amp, Ortec 113 The pre-amp integrates the pulse of charge from the photomultiplier and produces a voltage pulse proportional to the time-integral. The constant of proportionality is set by switch- selection of the integrating capacitor.
Delay Amplifier, Ortec 427A The unit accepts linear or logic pulses and produces a delayed duplicate of the input pulse. The delay time from input to output is the sum of the front panel switch settings.
Amplifier, Ortec 485 This unit accepts a voltage pulse of either polarity (switch selected) from the preamp and increases the magnitude by a set factor (COARSE GAIN, FINE GAIN). UNIPOLAR output is a positive pulse with specified time dependence, usually used for energy measurement. BIPOLAR pulses have a zero-crossing at a specified time after start and are useful in timing applications. The module also supplies electrical power for the pre-amp through a special cable.
B. Analog-digital interfaces Single Channel Analyzer, Ortec 488 The module detects input pulses which exceed a set threshold E (INTegral mode) or which fall into a range E to E + !E (DIFFerential mode). A switch allows recognition of either UNIpolar or BIpolar pulses. Both fast negative NIM and slow positive-NIM output pulses are provided. The time delay from input to output is adjustable from 0.1 to 1.1 μs.
Amplifier and Single Channel Analyzer, Ortec 490A, B The amplifier section accepts a voltage pulse of either polarity (switch selectable through side cover) from the preamp and increases the magnitude by a set factor (COARSE GAIN, FINE GAIN). Unipolar or bipolar output is switch selectable through the side cover. The SCA section produces a positive NIM output when the amplifier input pulse falls in a specified amplitude range. When the panel switch is set to DIFF, LOWER LEVEL sets the baseline and WINDOW sets the window width above the lower level. When set to INT, the LOWER LEVEL control sets a single threshold, and the WINDOW control is disabled. The module also supplies electrical power for the pre-amp through a special cable.
Discriminator, LRS 621BL This device accepts phototube pulses and produces fast NIM logic pulses. The output is triggered when the input crosses a preset threshold. Four independent discriminator circuits are provided in each module. The threshold is set with a screwdriver-adjust pot located behind the front panel. The threshold voltage, multiplied by a factor of ten, can be read with a voltmeter connected between the white-insulated monitor point and chassis ground. Each section of the module provides two pairs of coupled outputs, a single output and a single logical-complement output. If only one of the paired outputs is used, terminate the other member of that pair. Output pulse width is adjusted with the width pot. All outputs from a section are synchronous and have the same width.
C. Digital devices Gate and delay generator, Ortec 416A The module is triggered by a positive NIM logic pulse or by a fast negative NIM pulse. After an adjustable delay time, it produces a fast NIM pulse at the DLY'D MARKER output and an adjustable-width slow-NIM pulse of either polarity at the DELAYED OUT connectors. The maximum delay is set with a three position switch. A ten-turn pot selects a fraction of the maximum delay.
Universal coincidence, Ortec 418A The unit accepts positive NIM pulses at each of 5 inputs. Each input can be set for COINC, OFF, or ANTI. An output pulse is produced when the number of COINC inputs set by COINCIDENCE REQUIREMENTS are all positive within the resolving time of the module. A positive pulse at an input set for ANTI will prevent all outputs. Inputs set to OFF are ignored.
The various controls and inputs are used as follows:
START/STOP Fast NIM inputs GATE Slow-NIM logic input. TPHC accepts inputs when GATE is true (false) and switch is set to COINC (ANTI-COINC). If gating is not desired set to ANTI- COINC and leave input unconnected. STROBE Slow-NIM logic input. If set for EXT, TPHC produces output when STROBE goes true. If set for INT, output is produced at a fixed delay time after STOP signal. Delay time is set with OUTPUT DELAY. If strobing is not desired, set to INT and leave input disconnected. RANGE Product of RANGE and MULTIPLIER sets the full scale time range the TPHC will accept. AMPLITUDE Sets the pulse voltage corresponding to full-scale time interval. CONVERTER The output signal. A variable analog pulse at low- or matched-impedance. TRUE START Slow-NIM logic output. Indicates TPHC has accepted a START pulse.
Time Calibrator, Ortec 462 A time calibrator produces start and stop pulses separated by known time intervals. Since the pulse separation is determined by an accurate clock the device is useful for calibrating other instruments such as TPHCs. The outputs are fast NIM pulses from START and STOP. The time between start and stop pulses is n! where n is an integer and! is set with the PERIOD switch. The range switch determines the maximum n! produced. The repetition rate of START pulses is set with the RATE knob.
High-voltage power supply, Ortec 556 Caution : This module is connected to the AC line independently of the NIM bin. HV is present whenever the module switch is ON, even if the bin power is off. Output HV is the sum of the knob settings. The meter can be switched to read output voltage or current.
