PASCO TD-8565, Инструкция по эксплуатации и руководство по экспериментам

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012-05110C Adiabatic Gas Law Apparatus
3
Description of Apparatus
A piston, Fig 2, item a, made of acetal plastic is
manually driven down or up in an acrylic cylinder, Fig
2, item b, which is filled with any of several gases,
including monatomic argon, diatomic air or nitrogen,
triatomic carbon-dioxide, and other polyatomic gases,
which are injected and exhausted through the two
brass gas cocks, Fig 2, item c. Mounted on the side of
the piston is a linear potential divider, Fig 2, item d,
used to monitor the position of the piston. The 5 volt
source from the computer, or other low voltage source
available, is applied across the potentiometer element.
The voltage from the commutator brush, Fig 2, item e,
is then used to indicate the position of the piston and
thus the volume of the confined gas.
The acetal base, Fig 2, item f, which seals the bottom
of the cylinder has two transducers mounted on it.
Sealed against the lower surface of the base is a solid
state pressure transducer. The active element of the
transducer is a piezo-resistive device which forms part
of a bridge circuit. Mounted in the cylinder on the top
of the base is the temperature sensor, Fig 2, item g.
The active element is an extremely fine nickel wire
which has a very high temperature coefficient of
resistance. The fine wire also has a high surface to
mass ratio which allows its temperature to change
rapidly as the gas compresses or expands. (However,
there is still a small delay or time lag.) This wire is
also one arm of a bridge circuit. The electronic
circuitry of the apparatus consists of two excitation
voltage supplies and appropriate amplifiers for the two
bridge circuits. The outputs of the amplifiers are
analog voltages proportional to the pressure and
temperature respectively.
➤ IMPORTANT : The temperature sensor, Fig
2, item g, on the cylinder and the commutator
brush, Fig 2, item e, associated with the volume
transducer are extremely fragile. There should
be no need to disassemble the cylinder. If it is
ever necessary, remove the commutator brush,
Fig 2, item e, at the top of the cylinder before
removing the piston. Next remove the base,
carefully avoiding any contact with the tempera-
ture sensor. Damage to the temperature sensor
will necessitate returning the equipment to the
manufacturer for repair and
re-calibration.
Figure 2, Cylinder
As mentioned above, the electronic circuit consists of
the two amplifiers with bridge excitation sources. The
electronics may be powered with an external "floating
ground" 10 V DC supply (current about 10 ma), or a
9 volt battery.
➤
IMPORTANT:
The negative input is not
chassis ground. The sleeves of the output jacks
are connected to chassis ground which is main-
tained at +4 volts relative to the negative external
input. For this reason the supply voltage from
your computer should not be used to power the
equipment if the computer voltage source and
inputs have a common ground.
A transparent millimeter scale, Fig 2, item h, on the
front of the cylinder facilitates direct measurement of
the initial and final piston position of "volume" to use
in the computations or to calibrate the volume data
acquisition. Two removable pins, Fig 2, item i , are
provided to vary the excursion of the piston by limit-
ing the motion of the piston lever. Holes to store the
pins when not used are provided directly above the
central label.