Magnetostrictive Level Transmitter

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Magnetostrictive LT KTEK AT200 calibration and working principle

abb level transmitter

Working Principle

A low energy pulse generated by electronics travels through the length of magnetostrictive wire. When this signal encounters a magnetic float having a magnetic field a return signal is generated from the exact location where the float intersects the magnetostrictive wire. A timer measures the time of generation of electric pulse and the return signal. This time difference is used to calculate the level of the float

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Calibration of magnetostrictive level transmitter

  1. 1.Level Output Calibration

Calibration can be changed with the unit pushbuttons, or with a HART communicator (for units with the HART option), or with the menu driven LCD readout (for units with LCD option).

Calibration Using the Pushbuttons

Setting the 4mA point:

-Establish a tank level of 0% or move the float to the desired 0% point

-Enter the calibration mode by pressing the UP&DOWN buttons together for 1 second.

-Press the DOWN button for 1 second to set the output at 4.00mA.

At200

Setting the 20mA point:

-Establish a tank level of 100% or move the float to the desired 100% point

-Enter the calibration mode by pressing the UP & DOWN buttons together for 1 second.

-Press the UP button for 1 second to set the output at 20.00 mA

1

Note: The above steps can be repeated as many times as required

 Float Inspection

The AT200 will detect and report the position of the float (within the level gauge) on its sensor tube as a level of fluid in the process. In order to measure the fluid in the process properly, the float must move freely up and down the level gauge chamber partially submerged in the liquid. If the float were to become damaged or stuck in the chamber, the transmitter will still report the float position regardless of the actual process fluid level. This, by definition, is a Dangerous Undetectable failure. To prevent this failure the float will need to be inspected for integrity and movement. Some gauges will have two floats mounted in the chamber. This inspection should be done on both floats.

1) Move the float up and down the length of the chamber using the process fluid or some other media. The float should move freely from the bottom of the chamber from one process connection to the other.

2) Remove the float from the level gauge chamber. Inspect the float for signs of excessive wear or damage.

3) Submerge the float in a container of water to check for leaks as air bubbles escaping from the float. The float is a sealed unit and any holes in the shell of the float could allow process fluid to seep inside.

Note: K-TEK floats are designed for different specific gravity ranges. The float may or may not float in the water. It may be necessary to hold the float under the water to perform this test. Upon completion of float inspection, place the float back into the level gauge chamber paying careful attention to the float orientation.

Transmitter Testing

The transmitter of the AT200 is designed to return a level indication and an output based on the position of a float in the level gauge chamber. If the transmitter is equipped with an LCD on the front of the electronics module the level and current output will be displayed.

1) Apply power to the transmitter using the typical loop wiring diagram

2) Move the float up and down the level gauge chamber.

3) Monitor the indication of the level on the LCD to make sure the indication corresponds to the float position

Note: It is possible for the AT200 to continue providing a 4-20mA output if the LCD display is not functioning properly. If the LCD indicator on an electronics module fails during normal operation, it is recommended that the electronics module be replaced at the earliest convenience. It will not be necessary however to shut down a transmitter or remove it from service based on an LCD failure.

4-20mA Output

The current output of the AT200 transmitter update at least every 110 milliseconds and be filtered through the user adjusted Damping. The maximum response time to a process change will be less than 110 milliseconds or the value of the Damping, whichever is greater.

  1. 1.Apply power to the transmitter using the typical loop wiring diagram

    2.Connect a multi-meter (set to read milliamps) to the transmitter using the “Meter” connections on the terminal strip.

    3.Move the float along the length of the probe and monitor the milliamp output on multi-meter.

    4.The output should indicate the float position based on the calibration range of the transmitter.

4-20mA Loop Check

– Without HART

With the transmitter installed, wired and powered in its field location, move the float up and down the length of the probe. Confirm the proper reading at the indication or control room side of the loop. Move the float using the process fluid or some other mechanical means. If moving the float is not possible, the loop may be checked using an independent device such as a loop calibrator.

– With HART communications

With the transmitter installed, wired and powered in its field location and power supplied to the loop, connect a HART handheld device to the loop across a 250 ohm resistor. Using the Loop Test feature of the HART handheld, drive the output of the transmitter to 4mA then 20mA. Confirm the proper reading at the indication or control side of the loop.

Minor adjustments to the output of the transmitter may be made using the DAC Trim (Digital/Analog Converter) feature.

For level transmitter related topics, click on the link below

https://kishorekaruppaswamy.wordpress.com/2017/12/19/magnetostrictive-level-transmitter/

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https://kishorekaruppaswamy.wordpress.com/2016/06/10/level-measurement-using-pressure-gauge/

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https://kishorekaruppaswamy.wordpress.com/2012/11/16/calibration-procedure-of-displacer-type-level-transmitter/

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