PASCO SCIENCEWORKSHOP 750, Инструкция, Страница: 3 / 6

3
012-06772A Science Workshop
®
750 Interface
Analog Input Channels
The 750 has three identical analog input channels.
Each has differential inputs; in other words, they are
like the inputs to a volt meter where neither lead is
connected to ground.
The voltage measured is the
voltage difference between the inputs. Each channel
has three software-accessible gain settings: 1, 10, and
100.
The maximum sample rate depends on which
channels are selected for measurement.
For the higher
rates, ScienceWorkshop samples a block of 2000 bytes
and then transfers the block. Once transfer of bytes to
the host has started the interface starts sampling a new
block.
This is called burst mode since there is a small
time interval when data is not being sampled. The
main use for this mode is for the virtual oscilloscope.
Table 1 shows the sampling constraints while using a
fast computer to record the data.
Table 1. Sampling Rate Constraints
Sample Rate # of Channels Comment
250 KHz 1 analog Burst mode
100 KHz 3 analog Burst mode
50 KHz 5 analog Burst mode
20 KHz 1 analog (5 analog) Continuous* (burst)
10 KHz 1 digital Continuous* (burst)
(5 analog)
< 100 Hz 5 analog Continuous 8x
oversample
(improved accur-
acy at < 100 Hz)
* Note: Continuous sampling with 5 channels selected
is not possible to sustain for more than a few seconds.
There are five analog channels from which to choose:
channels A–C, analog output voltage (at banana
jacks), and the analog output current.
Please note that
for continuous sampling, the speed of the computer is
a significant factor, especially if
ScienceWorkshop is
busy with many displays.
➤
Note: When a digital sensor has been selected, the
sampling rate does not depend on the number of
digital channels since they are sampled simul-
taneously at 10 KHz.
Built-in Function Generator-Amplifier
The 750 has a built-in function generator that is used
to output analog signals. These can be either AC
signals, such as sine and triangle waveforms, or a DC
signal ranging b/- 5 V.
For the AC
waveforms, of which there are 8 resident in Flash, the
frequency can range from 1 mHz (0.001 Hz) to 50
KHz and the peak-to-peak amplitude can be adjusted
from 0 V to +/-5 V with increments of 2.44 m V.
The
output voltage is calibrated at the factory to null the
offset voltage and set the full scale voltage.
Accessing Analog Output
There are two different ways in which to access the
analog output signal.
The first (the default method in
ScienceWorkshop) is to connect test leads to the
banana jacks. The signal produced is a power
amplified (unity voltage gain) version of the signal
present at the DIN connectors and can supply nearly
300 mA at +/-5 V.
The output current can be
monitored along with the output voltage. The second
is to use a CI-6552A Power Amplifier (which has a
voltage gain of 2 and delivers 10 W) and connect its
DIN plug to one of the analog channels, A–C.
Digital Event Sampling
The 750 can sample digital events for photogate
timing. The 750 uses hardware edge detection so that
it can capture either edge or both as events, a feature
that is useful for setting trigger conditions.
It can
count digital events from devices such as a Geiger
tube or a Rotary Motion Sensor.
Each channel has an
independent 16-bit counter. For motion sensing, either
single or dual, the internal counters and edge detectors
provide improved performance with less noise in the
measurement.
Operation Precautions
Do not block the ventilating louvres on the top and
bottom of the interface box during operation.