Instrutech VGC301A User Manual page 15

Instruction Manual
SET ATM
1. To set the atmospheric pressure reading (also known as the "span" adjustment), flow nitrogen gas into
your closed vacuum chamber to allow the pressure to rise to a known value above 400 Torr.
Alternatively, if your local uncorrected barometric pressure (air) is known, simply vent your vacuum
system chamber to expose the gauge to the local atmospheric pressure.
2. Go to the SET ATM screen. When the desired pressure is stable, adjust the displayed pressure reading
on the VGC301 to the known value using the INCR (increase) or DECR (decrease) keys. Press the
SAVE/EXIT key to save the new atmospheric (span) pressure value.
SET SP1 ON and SET SP2 ON
These setpoints correspond to the turn on points for each relay. The relays will turn on (energize) when the
pressure is below this value. [Factory default = 100 mTorr] If you are unable to increase the values of SP1 ON
or SP2 ON , you must first go to SP1 OFF or SP2 OFF and increase those values to a number higher than the
values of SP1 ON or SP2 ON you are trying to set.
SET SP1 OFF and SET SP2 OFF
These setpoints correspond to the turn off points for each relay. The relays will turn off when the pressure is
above this value. [Factory default = 200 mTorr] If you are unable to decrease the values of SP1 OFF or SP2 OFF,
you must first go to SP1 ON or SP2 ON and decrease those values to a number lower than the values of SP1 OFF
or SP2 OFF you are trying to set.
SET ADDR
This is the lower nibble of the one byte RS485 device address. Assuming the address offset (ADDR OFFSET) is
equal to 0, setting the ADDR to a 5 will make the address be 0x05 in hexadecimal. A 15 will set the ADDR to
0x0F in hexadecimal. Note that the address (ADDR) must be used even when sending RS232 commands.
[Factory default = 1]
ADDR OFFSET
This is the upper nibble of the one byte RS485 address. Assuming the address (ADDR) is 0, setting the address
offset (ADDR OFFSET) to a 5 will make the address be 0x50 hexadecimal. Setting the offset to 15 will make the
address be 0xF0 hexadecimal. [Factory default = 0]
BAUD RATE
This sets the baud rate for the RS485 and the RS232 serial communications. The baud rate can be set to various
values through the serial interface or via the front panel soft-keys. The parity can only be changed through the
serial interface command set. When this occurs, the current setting will be shown in the list of choices and can
be re-selected if changed. [Factory default = 19.2K baud]
InstruTech, Inc.
VGC301A Controller
Page 13