Emerson 350, 250 operation manual Configuration options must be chosen at quoting stage

A high-speed microcontroller is utilized in the design to process and calculate the elapsed time measurement. Accurate crystals are used for the time based to resolve sub-microsecond timing increments. The binary number, equivalent to the microseconds of the echo travel time is used to calculate the distance of the float and a corresponding digital signal is output. A basic block diagram describing the operation is shown below.

Figure 7. Basic Transmitter Block Diagram

Calibration routines are included in the software to the 0% and 100% points for any distance desired. Even reverse calibration is a simple task using the software routines. Reverse calibration is desirable if ullage instead of level is required, or when the probe is installed with bottom mount electronics.

The LTM-350transmitter has four output configurations.

Configuration options must be chosen at quoting stage.

1.Primary Level – The most basic version of this transmitter is that it computes the distance between the float and the detector from the elapsed time measurement. A specific interrogation pulse is applied to the waveguide. Any feedback signal received before and after this window is rejected as noise. Even signals received during the active window are evaluated and filtered so that only high integrity data is accepted. The conditioned signal is converted to a percent of full-scale number and a number representing the distance and output as a digital signal. (LTM-250/350)

LTM-350, via HART protocol only.

2.Primary Level and Interface Level – A second float may be added below the first, and the second output will be calibrated automatically. The second time interval is timed in the same manner as the first one and added to the first to derive the position of the heavier float. The two floats require a separation of approximately three inches. The float size, geometry, and magnetic strength all play a factor in how close the two floats can be without interfering with each other.

3.Primary Level and Temperature – An optional temperature sensor is embedded inside the bottom tip of the probe, and it is configured to be the third digital output of the transmitter, and comes factory calibrated for the operating range of -50C to 149C (-58F to 300F)

4.Primary Level, Interface Level, and Temperature – This options is called a ‘full- blown” unit and offers all three possible outputs.

A deadband of approximately three inches, next to the detector, is fixed in the software and the float is not permitted to enter this area. If this happens output readings maybe erratic or go to fail mode.

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