This ValveLink8.2 analog output graph shows the voltage resulting from
valve #7 (4.67V) opening at time 8.07 seconds, then valve #3 (3.43V)
opening with Mode #6, "1-On" active. This immediately closes valve #7
(0.33V). The output returns to "baseline" of 2.5 volts after each 10ms pulse.
Spill Sensor
A two-pin socket on the ValveLink8.2 back panel accepts a 3mm Molex
"Microfit" female plug for a spill sensor. The spill sensor circuitry watches
any wires plugged-into this ValveLink8.2 port for a drop in electrical
resistance representing a liquid spill. In perfusion work spills usually
occur when the chamber vacuum stops or the vacuum trap fills-up. The
spill sensor circuitry immediately closes all valves and begins blinking
all LEDs to notify you of the spill. The ValveLink8.2 remains in this state
until you press any button to override the spill. After you clear the spill
warning, you may immediately begin opening valves again.
AutoMate Scientific provides a spill sensor made of Mylar tape and two
closely-spaced copper contacts. When liquids cross this tape, they make
contact with both copper strips simultaneously and complete an electrical
path for the spill sensor circuitry. In this way a drop of liquid passing
the sensor strip appears as a sharp drop in electrical resistance between
the two, otherwise disconnected copper conductors. Even distilled water
will conduct enough current to trigger the sensor. The adhesive tape
is designed to be placed around the flat outside edge of your perfusion
negative pulse. The voltage is 2.5 ± (valve# x 0.31V). For example,
whenever valve 4 opens, a 10 millisecond pulse appears on the analog
output at 2.5 + (4 x .31) = 3.74V. When the same valve #4 closes, it creates a
pulse of 2.5 - (4 x .31) = 1.26V.
This graph shows the analog output voltage vs. time resulting from each
valve opening and closing twice.
ValveLink8.2 Modes #2, #3 and #6 (see next chapter) and the analog input
automatically close other valves when a new one is opened to insure that
only one liquid is flowing at a time. If the user opens a valve in this way,
then any others will close at the same time. In order to indicate valves
opening and closing simultaneously on the event marker output, the
controller will give a short voltage spike upwards representing the valve
which opened, and immediately spike downwards to the appropriate
voltage for the remainder of the 10 millisecond pulse to signify the valve
which closed.
Valve #5 closing =
2.5 - (5 x .31) = 0.95V
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