Figure 3-6: RS485 termination resistor
3.8.2 Earthing and cable screening
The SAM42 is a very sensitive acoustic noise detection device. The
noise generated by the sand hitting the metal pipe is what the
SAM42 uses to estimate sand production. Unfortunately, there are
other noise sources that might have a negative impact on the sand
measuring performance.
For the best noise rejection performance, the electronics inside the
SAM42 enclosure are isolated from the enclosure itself.
The SAM42 may be located in a noisy environment (electrical
noise). In order for this electrical noise not to interfere with the
measurement capabilities of the device, certain measures should be
implemented:
• The cable shield should be terminated inside the gland. The shield
will then connect to the SAM42 enclosure through the gland.
• A galvanically isolated RS485 adapter should be used to avoid
creating ground loops.
• In order to avoid ground loops, the complete system should be
connected to PE in only one point. If the pipes are connected to
earth, then there is no need for any extra earth connection. If the
pipes are not connected to PE or if the connection is poor, then
the sensor’s enclosure should be grounded (PE). Each installation
has its own particularities but noise issues can be avoided by
following the simple steps described above.
Quick Start Guide May2024
30 Emerson.com/Rosemount
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