Emerson Rosemount 8732 manual Hz Signal to Noise Ratio

Rosemount 8732

Reference Manual

00809-0100-4665, Rev AA August 2010

High Process Noise Parameters

Troubleshooting High Process Noise

The High Process Noise diagnostic has two read-only parameters. It does not have any configurable parameters. This diagnostic requires that flow be present in the pipe and the velocity be > 1 ft/s.

5 Hz Signal to Noise Ratio

Reads the current value of the signal to noise ratio at the coil drive frequency of 5 Hz. This is a read-only value. This number is a measure of the signal strength at 5 Hz relative to the amount of process noise. If the transmitter is operating in 5 Hz mode, and the signal to noise ratio remains below 25 for approximately one minute, then the High Process Noise diagnostic alert will activate.

37 Hz Signal to Noise Ratio

Reads the current value of the signal to noise ratio at the coil drive frequency of 37 Hz. This is a read-only value. This number is a measure of the signal strength at 37 Hz relative to the amount of process noise. If the transmitter is operating in 37 Hz mode, and the signal to noise ratio remains below 25 for approximately one minute, then the High Process Noise diagnostic alert will activate.

The transmitter detected high levels of process noise. If the signal to noise ratio is less than 25 while operating in 5 Hz mode, proceed with the following steps:

1.Increase transmitter coil drive frequency to 37 Hz (refer to “Coil Drive Frequency” on page 4-13)and, if possible, perform Auto Zero function (refer to “Auto Zero” on page 4-12).

2.Verify sensor is electrically connected to the process with grounding electrode, grounding rings with grounding straps, or lining protector with grounding straps.

3.If possible, redirect chemical additions downstream of the magmeter.

4.Verify process fluid conductivity is above 10 microsiemens/cm.

If the signal to noise ratio is less than 25 while operating in 37 Hz mode, proceed with the following steps:

1.Turn on the Digital Signal Processing (DSP) technology and follow the setup procedure (refer to Appendix D: Digital Signal Processing). This will minimize the level of damping in the flow measurement and control loop while also stabilizing the reading to minimize valve actuation.

2.Increase damping to stabilize the signal (refer to “PV Damping” on page 3-11). This will add dead-time to the control loop.

3.Move to a Rosemount High-Signal flowmeter system. This flowmeter will deliver a stable signal by increasing the amplitude of the flow signal by ten times to increase the signal to noise ratio. For example if the signal to noise ratio (SNR) of a standard magmeter is 5, the High-Signal would have a SNR of 50 in the same application. The Rosemount High-Signal system is comprised of the 8707 sensor which has modified coils and magnetics and the 8712H High-Signal transmitter.

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