OTT PLS - Searching for Disruptions;Troubleshooting; SDI-12 Sensor Not Responding; Missing 4-20 mA Loop Current; Inconsistent or Missing Measured Values

8 Searching for disruptions/troubleshooting
Sensor does not respond to the SDI-12 interface
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Sensor correctly connected to a datalogger with SDI-12 input (master)?
➝ Correct connection assignment.
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Polarity of the supply voltage reversed?
➝ Correct connection assignment.
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Supply voltage < 9.6 V or > 28 V?
➝ Adjust level of voltage supplied (check the length and cross-section of the
connection cable).
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Is the supply voltage not direct current?
➝ Only operate sensor with direct current.
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Does the sensor address of the OTT PLS correspond with the sensor address
that the datalogger uses?
➝ Correct sensor address.
4 … 20 mA loop current is missing
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Is the sensor correctly connected to a datalogger or peripheral device with
4 ... 20 mA input (check polarity)?
➝ Correct connection assignment.
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Is the 4 .. 20 mA loop current correctly supplied through datalogger or OTT
PLS (internal/external supply)?
➝ Correct connection assignment.
Measured value varies or is not present
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Sensor dirty?
➝ Clean sensor carefully. See Chapter 7, "Carrying out maintenance work".
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Installation of the sensor steady (e.g. movement from swell)?
➝ Optimize installation.
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Drops of water in the pressure compensation capillary?
➝ Replace pressure probe.
Status output at the 4 … 20 mA interface
The OTT PLS with 4 … 20 mA interface indicates the operational state or any
faults that might occur via the loop current:
Loop current Status
4 … 20 mA correct
3.4 mA FLASH memory defective
3.3 mA Watchdog error
3.2 mA Failed memory
3.1 mA Pressure cell defective
3.0 mA Analog converter defective
<3.0 mA Loop current error: broken line, loop supply missing
3.6 mA Measurement range not reached (underflow)
or global error
3.8 … <4.0 mA Marginally below measurement range: The pressure
probe delivers an output signal proportional to the
water level, but is outside the specification (under range)
>20.0 … 20.5 mA Marginally above measurement range: The pressure
probe delivers an output signal proportional to the
water level, but is outside the specification (over range)
21.0 mA Measuring range exceeded (overflow)
Status output at the SDI-12 interface
see SDI-12 command aM1!
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