Xylem H-3342 - Manual (Page 10)

2-2 Installation
H-3342
2.2 4-20mA Output
Current loop sensors output a current rather than a voltage. The 4-20mA output will drive
standard industrial telemetry and process control instrumentation. Since the signal to noise
margin of 4-20mA is not large, take care to protect the wiring from noise and interference. The
loop power supply must be sufficient to maintain 8.5 to 35 Volts across the H-3342's output
terminals, in addition to whatever voltage is needed to maintain 20mA across the loop receiver
and interconnect wiring. The +12.0V SDI-12 power source will work if the resistance of your
loop receiver and wiring is less than 150 ohms.
8.5V + (150ohms * 20mA) = 11.5V
The 4-20mA output is reverse diode protected.
! Make certain there is 8.5 to 35V across the 4-20mA output terminals.
! Make certain the H-3342 is receiving +12V power from the SDI-12 bus.
! Use shielded 4-20mA cables in noisy environments.
2.3 Programming Your Data Recorder
You must prepare your data recorder to receive and record the H-3342 data. Since data recorders
differ widely, refer to your recorder manufacturer's directions. In general, program the data
recorder to input three values via the SDI-12 port. Usually only one or two of the parameters is
actually recorded. Your data recorder must issue an “aM!” command, then collect the data with a
“aD0" command, as explained in Chapter 3. The H-3342 places three parameters in its data
buffer:
a+BB.BBB+CC.CCC+D
Where:
a = Is the SDI-12 address 0-9, A-Z
BB.BBB = Stage in user units of Feet, Meters etc.
CC.CCC = Raw encoder position in units of revolutions (turns)
D = Encoder status:
0 = no error
1 = not enough light
2 = too much light
3 = misalignment or dust
4 = misalignment or dust
5 = misalignment or dust
6 = hardware problem
7 = fast mode error
8 = multi turn position not initialized
15 = no response from the encoder (data is unusable)
16 = turn counter error (data is unusable)