LEYBOLD IONIVAC ITR 90, Operating Manual

Page: 31 / 50

Operation
GA09420_002_C0 – (2016-10) –

Leybold 31
Calculation of the pressure value
The pressure can be calculated from bytes 4 and 5 of the transmitted string. De-
pending on the currently selected pressure unit (
→
byte 2, bits 4 and 5), the ap-
propriate rule must be applied.
As result, the pressure value results in the usual decimal format.
p
mbar
= 10
((high byte × 256 + low byte) / 4000 - 12.5)
p
Torr
= 10
((high byte × 256 + low byte) / 4000 - 12.625)
p
Pa
= 10
((high byte × 256 + low byte) / 4000 - 10.5)
Example
The example is based on the following output string:
Byte No 0 1 2 3 4 5 6 7 8
Value 7 5 0 0 242 48 20 10 69
The instrument or controller (receiver) interprets this string as follows:
Byte No Function
Value Comment
0 Length of data
string 7 (Set value)
1 Page number 5 ITR 90
2 Status 0 Emission = off
Pressure unit = mbar
3 Error 0 No error
4
5
Measurement
High byte
Low byte 242
48
Calculation of the pressure:
p = 10
((242 × 256 + 48) / 4000 - 12.5)
= 1000 mbar
6 Software version 20
Software version = 20 / 20 = 1.0
7 Sensor type 10 ITR 90
8 Check sum 69
5 + 0 + 0 + 242 + 48 + 20 + 10 =
325
dec
≙
01 45
hex
High order byte is ignored

Check sum = 45
hex
≙
69
dec
4.6.1.2 Input String (Receive)
For transmission of the commands to the transmitter, a string (frame) of five bytes
is sent (without <CR>). Byte 1 to byte 3 form the data string.
Format of the input string
Byte no Function Value Comment
0 Length of data string 3 (Set value)
1 Data
→
admissible input strings
2 Data
→
admissible input strings
3 Data
→
admissible input strings
4 Check sum
(from bytes No 1 … 3) 0 … 255
(low byte of sum)
1)
1)
High order bytes are ignored in the check sum.