Features

• Eight inputs per unit, up to 32 inputs with multiple 8224's
• Compatible with 8700/ 9600 Series ADCs
• Switch selectable group size from 256 to 8K channels
• Separate live and real time clocks for each input
• Ideal for use in low count rate applications such as environmental analysis and alpha spectroscopy
• Independent or simultaneous start/stop control of inputs

Description

The Model 8224 Analog Multiplexer (AMX) Module allows multiplexing of up to eight analog input signals through a single analog-to-digital converter (ADC).

Two 8224 modules may be used to handle up to 16 input signals per ADC, simultaneously. Internal DIP switches allow the user to select the group size, number of active inputs, module number assignment and master/slave designation of each 8224 in a system. These switches are accessible by removing the side panel of this dualwidth NIM module. Multiplexing provides a cost effective method of handling a large number of low count rate input signals with one ADC, and is ideal for environmental analysis and alpha spectroscopy applications. When used with a fast ADC, such as the Model 8715 900 ns Fixed Dead Time ADC, the Model 8224 provides cost effective multiple-input capability with good count rate performance.

The Model 8224 contains one Peak Detect and Hold (PDH) circuit for each of the eight input signals. These analog memory circuits hold the peak value of each input pulse as a dc voltage level. The Model 8224's internal logic continuously scans the status of the eight PDH circuits at a rate of 500 kHz. When one of the PDH circuits captures a pulse, the scanner stops and connects the PDH to the ADC input. The 8224 then generates a gate pulse which initiates the ADC conversion cycle. When the conversion is complete, scanning resumes. Each event processed by the ADC is automatically routed into the associated memory group by appending routing bits to the digital ADC output word.

Each of the eight inputs to the Model 8224 is assigned a specific group size. For example, if the MCA is configured to provide 8192 channels of memory, and the 8224 is configured to provide eight 1K groups, data from Input 1 is stored in the first 1024 channel group, data from Input 2 is stored in the second 1024 group, and so on. This results in eight individual spectra, each representing one input signal, effectively simulating an individual ADC processing each input.

In addition, the Model 8224 provides live and real time clocks to accurately indicate the acquisition time for each group. The elapsed live and real time in seconds is accumulated in the first two channels of each group.

Lower Level Discriminator (LLD) adjustment for all eight input signals is provided by a common front panel control.

Analog multiplexing can be performed in an external trigger mode which allows processing of dc voltage levels applied to the 8224's inputs. In this mode, each time a positive trigger signal arrives at the rear panel Trigger input, the 8224 takes a snapshot of the voltage levels of all active inputs. One event is acquired in each group with each trigger signal.

External control of each input (start/stop) can be provided by Genie 2000 or Genie-ESP System Software. The MCA System also requires a parallel interface for individually controlling each input. This is provided by the Model 880777/554 RPI module when used with the Model 556A AIM MCA module.