from low to high, that valve opens. Then the ValveLink8.2 ignores that
input until it changes (high back to low) again. If that valve's manual
pushbutton is pressed, it toggles the valve from open to closed or vice
versa - regardless of the state of its other inputs. Therefore, whichever
input happens last determines the state of the valve.
LED Indicators and ValveGuard
™
The eight numbered valve LEDs on the front of the ValveLink8.2 give you
the current status of each valve. They can each be in one of four different
states:
Red = Valve plugged-in but closed
Green = Valve plugged-in and open
Off = No valve plugged-in or broken valve wire
Flashing red = Short-circuit detected in valve wire
These last two states represent our ValveGuard technology. Special
circuitry detects a good valve resistance or short-circuit. Broken or shorted
(crossed) valve wires used to be the biggest cause of valve failure and
controller damage. Now these two problems are easily observed and
isolated before they can damage the controller. See the "Valve Cables"
section in the "Techniques" chapter later in this manual to repair a broken
valve cable yourself.
Press the valve button to clear a flashing short signal and try opening the
shorted valve again. If all LEDs are flashing it means the spill sensor has
been tripped. See the Spill Sensor section below. The ValveLink8.2 will not
even try to open a valve which is not plugged-in (its LED is off).
Event Marker
The ValveLink8.2 outputs a 10 millisecond voltage pulse on its front-panel
analog output BNC as an event marker every time a valve opens or closes.
The marker voltage occurs regardless of how the valve was opened or
closed (i.e. manual pushbutton or computer digital input). This voltage
can be easily recorded with a single channel of your data acquisition
software for a permanent, synchronized record of valve activity. Here are
the voltages sent by the ValveLink8.2:
+2.5 volts is the baseline when nothing is happening. Valves opening
create a 10 millisecond pulse upwards, while closing valves cause a
Digital Input Port Pin-out
[Back panel diagram view]
Standard female DB-9 connector
pin#
pin#
1 = ground
6 = TTL8
2 = TTL7
7 = TTL6
3 = TTL5
8 = TTL4
4 = TTL3
9 = TTL2
5 = TTL1
AutoMate Scientific sells BNC cables with four or eight TTL inputs
wired to BNCs for you. Parallel port and Heka EPC / ITC cables are
also available.
Analog Input
The front panel "Analog Input" BNC accepts a 0-5V DC signal to open a
valve using only a single analog output from your computer. Here are the
voltages it accepts:
0 (zero) volts = All off
Ch 1
2
3
4
5
6
7
8
Voltage 0.5
1.1
1.6
2.1
2.7
3.3
3.9
4.6V
Changing from one voltage to another closes ALL other valves.
Simultaneous Edge-triggered Inputs
You may be wondering how the ValveLink8.2 can respond to so many
inputs simultaneously -- digital, analog and pushbuttons all at the same
time. If a digital input is "high," then shouldn't that valve be open? How
can you close it by pushing the button? The answer lies in an electronics
concept called "edge triggering." Rather than watching the state of an
input (i.e. high or low TTL input), the ValveLink8.2 watches for a change in
state (i.e. rising or falling edge of TTL input). When a TTL input changes
1
5
9
6
19
18