INFICON BCG450 ATM to Ultra-High Vacuum Triple Gauge - Manual (Page 31)

tina40e1-b (2011-04)
31
The following diagram shows the functional principle using example values
(italic = example values):
833 mbar
816 mbar
1500 mbar
980 mbar
Measuring signal
(Pressure p)
Atmospheric pressure (100%, ambient) 2)
Atmospheric pressure
threshold (85%)
Hysteresis
(2% of atmospheric
pressure threshold)
Upper limit of measuring range of gauge
M
ea
su
red
va
lue
Relay status "Atmospheric pressure reached"
Programming the atmospheric pressure threshold can only be carried out via the
serial interfaces.
The relevant parameter: percentage of atmospheric pressure (N) is sent to the
gauge in a 5 byte long command string (general information on RS232 interface
→ 33):
Byte No. Function Value Comment
0 Length of data string 0x03 hex set value
1 Data 0x11 hex
2 Data 0x10 hex
3 Data 0x01 … 0x8C hex 1)
4 Check sum
(of bytes No. 1 … 3)
0x00 … 0xFF hex low byte of sum, high
byte is ignored
1) Admissible range of percentage value (N):
0x01
hex
… 0x8C
hex
= 1
dec
… 140
dec
= 1% … 140% (default = 99%).
Example:
Atmospheric pressure = 1000 mbar (example) 2)
N = 99% (default)
Hysteresis = 2% (fixed)
⇒ Atmospheric pressure threshold = 990 mbar
⇒ If the pressure exceeds 990 mbar, the relay "Atmosphere reached". is
activated. As the pressure drops below 970 mbar, the relays is deacti-
vated.
2) It is possible to calibrate the atmospheric pressure sensor ( → 45).
The definition of the function assigned to the relays (SP A/B or "Atmospheric pres-
sure reached") and the value "Percentage of atmospheric pressure" (N) is descri-
bed in the communication protocol of the respective interface version (for
DeviceNet
→ [1], for Profibus → [2]).
Example
4.6.2 Programming the
Atmospheric Pressure
Threshold
Programming via RS232
Programming via fieldbus
interfaces