Emerson Process Management rosemount 3300 series Example 1 amplitude threshold T2 is too high

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00809-0100-4811, Rev AA October 2002

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Figure 6-10. Example 1: amplitude threshold T2 is too high.

Figure 6-11. Example 2: amplitude threshold T2 is too low.

Rosemount 3300 Series

The amplitude thresholds are automatically adjusted to appropriate values in order to filter out noise and other non-valid measurements from the measurement signal.

The amplitude of the measurement signal, i.e. the amplitude of the signal that is reflected by the product surface, is related to the actual dielectric constant of the product. The amplitude threshold that is used by the transmitter is

based on the parameter configuration of the current product dielectric constant (see 6HFWLRQ ￿￿￿%DVLF￿&RQILJXUDWLRQ). Normally no other threshold

adjustment is needed, but if the transmitter still does not track the product surface correctly it may be necessary to adjust the threshold values.

The Radar Configuration Tool (RCT) has a plot function allowing you to view the reflections along the probe.

If the amplitude threshold is too high the product level is not detected as illustrated in Figure 6-10.

	100		(+￿￿!￿"￿￿￿;￿"￿￿￿￿￿￿				250
	80					T3	200	HIGH
	60
Amplitude	-20				T2			THRESHOLD
	40						150
	20
	0						100
		T1					50	WAVEFORMPLOT
	-40
			P1
	-60
							0
	0	100	200	300	400	500	600
				Distance (samples)

If there are disturbing objects in the tank the threshold must be carefully set in order to avoid locking on the wrong amplitude peak. In Figure 6-11the transmitter has locked on a peak above the actual product surface, i.e. a disturbance was interpreted as the product surface, whereas the actual product surface was interpreted as an interface or the probe end.

	100	$￿￿￿￿￿￿￿￿￿;￿￿￿￿￿￿￿￿￿			P3	￿￿￿￿￿￿￿￿￿￿￿￿￿￿	T3		250	LOW
	80
	60								200	THRESHOLDWAVEFORMPLOT
Amplitude	40				P2				150
	20
							T2
	0								100
	-20		T1
									50
	-40
			P1
	-60
									0
		0	100	200	300	400	500	600
					Distance (samples)

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