How To Use the Remote Zero Feature Cha
ter Five: O
eration
80
How To Use the Remote Zero Feature
The I/O connector provides the ability to zero the 670 instrument remotely. The 670 instrument
uses an edge trigger to activate the remote zero function. Edge triggering requires that pins
change from one state to another before the function will occur. The function will not be
repeated until the
transition
occurs again. The pins on the I/O connector float high when open
(disconnected). To activate the remote zero feature, pull the pins low (transition from high to
low). Refer to
The [ZERO] Key,
page 62, for information on the zero function.
1. Check that the zero feature is enabled.
If you are using remote communications, send the appropriate command to enable the
zero. If you are in
LOCAL
operation, press the [
ZERO
] to check the state of the zero
function. Adjust if necessary.
2. Place the Key Lock switch, located on the front panel, in the
REMOTE
position.
3. Pump down the system to a pressure less than the resolution of the pressure transducer.
To achieve a proper zero, the pressure of the system must be
less
than
the resolution of
the pressure transducer used to measure the system pressure. The transducer will not be
zeroed if the output of the transducer is greater than 2% of the sensor full scale range.
Refer to the pressure transducer instruction manual for the proper pressure for your
transducer. It may take several hours to achieve an acceptable base pressure.
4. Connect pin 12 (remote zero) to pin 4 (digital ground) on the I/O connector and hold the
connection for at least 200 milliseconds.
The remote zero function uses edge triggering so that the command is only executed
once when the remote zero pin is brought low. If you need to repeat the zero procedure,
you must release the connection for 200 milliseconds, to allow the line to float high.
When you reestablish the connection, the line will be pulled low again, and the
instrument will perform the zero function.
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