iRIS 220 / iRIS 320, V1.19 User Guide - 66
SDI-12 Electrical Interface
The
1)A serial data line
2)A ground line
3)A
In the following specifications, all values not indicating specific limits have an allowable tolerance of ±10% of the value. The
Serial Data Line
The data line is a
Condition | Binary state | Voltage range |
Marking | 1 | |
Spacing | 0 | 3.5 to 5.5 volts |
Transition | undefined | 1.0 to 3.5 volts |
Table 1. Logic and voltage levels for serial data
Voltage Transitions
During normal operation, the data line voltage slew rate must not be greater than 1.5 volts per microsecond.
Ground Line
The ground line must be connected to the circuit ground and the earth ground at the data recorder. The sensor circuit ground also must be connected to the ground line, but not normally to its own earth ground. If it is necessary to connect the sensor circuitry to earth ground, a heavy (12 AWG or larger) ground wire should be connected between the sensor earth ground and the data recorder earth ground for lightning protection.
The ground conductor should be large enough to keep the voltage drop between the data recorder and all sensors less than 0.5 volts during the maximum combined sensor current drain.
12 Volt-Line
The data recorder (or the external power supply) provides between 9.6 volts and 16 volts to the
Note: This information is taken from:
Version 1.3 – September 17, 2002
Prepared By
(Technical Committee)
66 | iQuest (NZ) Ltd - PO Box 15169, Hamilton, New Zealand Tel: +64 7 |
