.
6. Accessory I/O
On the middle right side of the instrument rear panel is
the 24 pin card edge connector, marked
‘ACCESSO
RY
INPUT’
or ACESSORY INPUT OUTPUT (on newer
models). This connector permits access to circuitry for test
purposes, as well as for special user functions. The two
most important functions are remote control and auxiliary
power, as described below.
6.1 Remote Control
Remote operation for continuous wave (D.C)
measurement s requires only the RS232C port, with the
function set to the auto-range mode. Data will be
transmitted when requested via the RQS (ReQuest to Send)
line on that interface.
Flash measurement s require more control over, and
coordination with the instrument, through the
‘ACCESSO
RY
POR
T’
. Either external switch control or standard computer
logic will activate the four functions equivalent to the front
panel push buttons. The (inverted) FLAS output, goes low
once the ILT1700 is ready to integrate. This logic level can
be used to trigger the flash lamp, or
‘handshake’
with a
computer device to complete a two way protocol. The
following is a list of user inputs:
Pin#
Mnemonic
True Level Description
10
/ZERO
Low
Zero (not)
L
/SWDN
Low
D.C. (not)
J
/INTG
Low
Integrate (not)
K
/HOLD
Low
Hold (not)
9
/FLAS
Low
Flash (not): output
If mechanical activation is required, a switch closure
between any of the above listed inputs, with respect to
ground, will activate that function. It is only necessary to
keep the switch closed for 50 milliseconds to assure
sampling response from the internal computer. Contact
bounce less than 1 millisecond is allowed for reliable
operation.
Digital logic, or the output from a computer user port,
can be used if it is TTL compatible or if the drive can
‘sink’
at least 1 milliamp, to a voltage level below 0.8 volts, and
allow the level to rise above 3.5 volts (essentially no
sourcing necessary) upon release. The low state is the
‘true
level
’
in each case. The description, on the previous chart,
shows which function key the low state will equate to.
When the ILT1700 is ready to integrate, it will pull pin 9
to a voltage level less than 0.8 volts (assuming the current
load is less than 1.3 mA). This occurs in less than 8
milliseconds after /INTG is pulled low. That line can be
used to activate a flash lamp for fully automatic operation.
A fully automatic system would pull
‘/ZERO’
low as
part of the initializatio n routine to cancel out any ambient
conditions. Some time later, when a test lamp was in
position,
‘/INTG’
would be pulled low for more than 50
milliseconds, or until
‘/FLASH’
was sensed. Three seconds
after that
‘/HOLD’
would be pulled low for 50 mS, and RQS
would be sent to the RS232C port until serial data begins to
be received. The data would be processed, and a new lamp
would be inserted in the test station, and
‘/SWDN’
would be
pulled low to zero out the integration register.
‘/INTG’
would be pulled low again to start the next cycle, and so on.
The
‘AU
TO-RANGE
’
feature should be on to handle any
magnitude of light source, and the
‘5
V BIAS
’
generally
should be on to increase the detector speed and to handle the
large instantaneous charge from the flash.
6.2 Test Pins
There are accessory pins that are used during the
system test at the factory, but a user normally will not be
concerned with any of these except possibly for pin 11
(VRAM), which tests the
‘kee
p alive
’
voltage for the
continuous memory. This should be greater than 2 volts
when measured with a high input impedance volt meter, with
respect to ground (found on pins A, or 1). Pin 3 is the +5
volt logic power supply voltage, which can be used for
external logic as long as it draws less than 50 milliamps.
6.3 DC Power
When the internal batteries are used, the instrument
automatically turns itself off after about 6 minutes. For
field testing, continuous measurement s may be desired or it
may be beneficial to recharge the internal Nickel-Cadmium
batteries from a mobile power source. In either case the
Auxiliary input can be used as found on pin C. This
auxiliary D.C. (direct current) power must have a potential
b8 and +15 volts with respect to the ground pins(A
or 1). This range was chosen to permit use of normal
mobile power. We offer an accessory called the A401,
which provides a cigarette lighter plug, cable, and accessory
connector for such mobile use. If mobile power is not
available, the instrument may be operated from any 12 volt
battery capable of supplying 380 milliamps for the duration
of the experiment.
6.4 Analog Output
An analog output pin is available on t he accessory
connector. It is brought out on pin 8, which uses any of the
ground pins 1, A or N, as the signal return path. This signal
called RECO.
7. Precautions
The ILT1700 has been designed to minimize problems
due to improper operation of the instrument. From our 40
years of manufacturing instruments, we have found a few
abuses that can cause trouble, as follows:
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