Ampcontrol Pty Ltd
– ABN 28 000 915 542
GG2 DISPLAY USER MANUAL
GG2B023 Version 3
– JUNE/19
Uncontrolled Copy - Refer to Ampcontrol Website for Latest Version
Page 53 of 82
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6.4 External Interfaces
Gas Reading Units
As the protocols Modbus and iMAC are both limited to 16bit wide data registers, a system has been
used to encode
the current gas reading of the device. The readings are transmitted in units of ‘permyriad
of full-
scale’. A permyriad is 1/10000 (one ten thousandth) and can be denoted with a
‱
symbol. The
relationship between the real world units (e.g. PPM, %) and the permyriad is as follows:
𝑅𝑊𝐺𝑉 = 𝐺
0
+
𝑇
𝑝
10 000
× 𝐺
𝑠
Where:
𝐺
0
= gas zero value (i.e. 0% v/v)
𝐺
𝑠
= gas span value (i.e. 5% v/v)
𝑇
𝑝
= transmitted permyriad value (i.e. 123
‱)
𝑅𝑊𝐺𝑉
= Real World Gas Value (i.e. 1.25% v/v)
These permyriad values therefore correspond to different gas concentrations on different detectors.
Some example values are calculated in the following table.
Table 9: Example of Permyriad to Gas Concentration Conversion
Gas Range and Units
Permyriad (
‱)
0-5% v/v
0-100% v/v
0-10 ppm
-100
‱
-0.05% v/v
-1% v/v
-0.1 ppm
0
‱
0% v/v
0% v/v
0 ppm
5000
‱
2.5% v/v
50% v/v
5 ppm
10000
‱
5% v/v
100% v/v
10 ppm
10100
‱
5.05% v/v
101% v/v
10.1 ppm
Protocol Selection
Before a protocol can be configured it must first be selected as the active protocol. Protocol selection
must be done via the “PROTOCOL SELECT” screen in the configuration menu, refer to Section 6.3.2.
The options are:
IMAC
MODBUS, or
NONE
For general guidance on editing options please refer to Section 6.1.2.2.
Modbus
6.4.3.1 Configuration
After selecting the Modbus protocol, it may be configured. Protocol configuration must be done via the
“PROTOCOL CONFIG” screen in the configuration menu. Within this menu, there is a single option -
SETTINGS. For general guidance on editing options please refer to Section 6.1.2.2.
