For high light level experiments
we recommend the photodiode array imaging system. Since photodiodes
do not saturate at high light intensities this system is well
suited for fluorescence measurements from bulk stained tissue
and for absorption measurements.
The NeuroPDA-III uses the WuTech®
H-469V photodiode array. The new H-469V photodiode array (PDA)
performance is very similar to the previous array used in the
NeuroPDA system. Using surface mount technology and low power
consumption components the entire circuitry of the H-469V (The
diode array, first and second stage amplifiers and multiplexer)
fits inside one smaller box. (
Compare size of H-469IV and H-469V)
This arrangement eliminates the need for an amplifier rack and
the heavy cable bundles used with previous generations of the
PDA. The new systems are much more compact, much lighter and
easier to handle and ship. Moreover, they are much more reliable
and easier to operate as problems like 60 Hz line noise, oscillations
and ground loops are eliminated.
Dynamic Range
More than 18 bits (100 db); the system
can record signals as small as 10-5 of the resting light level.
Frame Rate
The photodiode array system was designed
for high speed data acquisition: 1.6 Kfps (including 464 diodes
and 8 electrodes). The user can sample a subset of the array
to further increase the frame rate.
Dark Noise
Low, close to the Johnson noise of
a 100 M-ohm resistor.
Signal-To-Noise Ratio
Near optimal signal-to-noise ratio
for a broad range of light levels. Silicon diodes have quantum
efficiencies near 1.0. Unlike a CCD camera, the photodiodes
do not saturate at light intensities achieved in some neurobiological
experiments. Base-line subtraction (AC coupling) in individual
channels offers an effective A-to-D resolution of more than
20 bits with the 12 bit A-to-D converter.
Comprehensive Software Designed
With Neurobiology and Physiology In Mind
Neurobiologists typically analyze voltages
using electrodes. The software includes the data format that
neurobiologists are used to analyzing - wave forms over time
for each photodiode input. NeuroPlex also creates pseudo-color
images and "movies". Further, the system provides
8 BNC inputs sampled and displayed with the photodiode data.
A mouse driven point-and-click interface shows multiple views
of the data for clarity and simplicity. Comprehensive analysis
capability is provided.
Integrated System
Includes all the necessary components
from the photodiode array through the data acquisition and
processing unit (diode array, amplifiers, multiplexers, analogue-to-digital
converter, computer, and output control panel).
Experimental Control
The system can control a shutter and
a stimulator. Three kinds of triggering for data acquisition/averaging
are available:
1. Triggered by user/computer.
2. Triggered by an external event.
3. Triggered by an event recorded on one of the 472 channels.
Hardware
Overview
The following are the components
of WuTech H-469IV
464 Element Diode Array:
Fiber
optic bundle tightly packed at the image plane leads to
individual photodiodes. Photodiode specifications include:
dark current less than 10 pA, shunt resistance greater than
50 G-ohm, radiant sensitivity (630nm) 0.42 A/W and terminal
capacitance 30 pF.
· For more information
about the array
Pre-amplifiers:
The current-to-voltage converter has
three selectable feedback resistors on each channel (5, 50
and 500 M-Ohm), offering a choice of gains for the first stage
(pre-amplifier). The 500 and 50 M-Ohm are appropriate for
measurements with fluorescent dyes in single cells. The 5
M-ohm resistor is intended for use with absorption dyes and
bright fluorescent preparations.
Post-amplifiers:
The post-amplifiers (second stage)
offer amplification of 1,10,50 and 500 fold. They also contain
a 2-pole RC low-pass filter of 800Hz and an AC high-pass filter
with a choice of 2 time constants (200 msec and 2,000 msec).
Defective Channels:
The delivered system is specified to
have fewer than 3% defective channels (typical, fewer than
1%). The NeuroPlex software allows the user to deal will defective
channels in two ways: 1) by substituting the data in a defective
channel by the average of the data from the neighboring detectors
(Fudge Array) or 2) by replacing the data from that channel
with a flat line (Omit Array).
Multiplexer and Analog-to-digital
Converter:
512 channel multiplexer and A-to-D
converter with 12 bit resolution.
Input/Output Panel:
Includes 8 electrode BNC inputs and
16 output BNC connectors to control a shutter and a stimulator.
The input channels are sampled and displayed with the data
from the diode array.
Power Supply:
Provides DC power for all components.
Computer:
PC computer for acquisition and analysis,
Monitor not included. We recommend at least 1280x1024 (17
inch) resolution. 1600x1280 (21 inch) is also supported.
*The hardware is manufactured by WuTech
Instruments. It is a 3rd generation commercial version of
the diode array system developed by the electronics shop of
the Department of Physiology, Yale University School of Medicine
(New Haven, CT).
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