Thyracont VSH88D, Operating Instructions Manual

Page: 45 / 56

45
vsh-de-130326
4.6 Gas-Correction-Factors
The output signal of the VSH depends on type and composition of the gas being
measured. The unit is adjusted for N
2
and dry air. For other gases the pressure
display can be corrected below 0.1 mbar by setting correction factors for both
sensor types via RS485.
The measurement results of both sensors are then individually multiplied with the
corresponding correction factors by the units microcontroller. The VSH can
thereby provide a corrected pressure signal as analog and digital output.
Correction factor 1 Pirani:
Ar
1,6 CO
2
0,89 He 1,0 Ne 1,4
CO 1,0 H
2
0,57 N
2
1,0 Kr 2,4
Correction factor 2 Bayard Alpert:
Ar
0,80 H
2
2,4 N
2
1,0 Kr 0,6
CO
2
0,74 He 5,9 Ne 3,5 Xe 0,41
Address Code Data cks CR
Address:
3 Bytes, decimal; address space RS485: 001 – 999
Code: "C" for reading, "c" for writing a correction factor
Data: Query to read or unlock: 1 Byte; "1" for correction factor Pirani,
"2" for correction factor Bayard Alpert
read or write: 6 Byte; unsigned int
cks: 1 Byte, checksum, defined as sum over all Bytes of the fields
address, code and data, modulo 64 plus 64.
CR: Carriage Return (0Dh, 13d)
The value in the data field when reading or writing correction factors contains
leading zeros and is equal to the 100fold of the factor. Range: "000020" for 0.20
to "000800" for 8.00
Example (for address-switch in position "1"):
Action Telegram to
transducer Answer telegram
from transducer
Read gas correction factor 2 "001C2F
C
R
" "001C000240z
C
R
"
c2=2.40
Unlock gas correction factor 1
Set gas correction factor 1
to 0.57 "001c1e
C
R
"
"001c000057`
C
R
"
"001c1e
C
R
"
"001c000057`
C
R
"
Please find further information about the Thyracont communication protocol in
chapter 4.2.