Skip to main content

Nuclear Level Detectors Cascade or Master/Slave concept

A typical Nuclear / Nucleonic source and detector level measurement is shown in Below Fig 1. 

In certain process applications, the vessel or tank level measurements may vary from 2 mtrs to 30 mtrs or more.  In the Nuclear / Nucleonic Level Instruments, detectors are available with standard lengths varying from 2 meter to 6 Meter. Standard length varies from supplier to supplier from 2 mtrs ~ 6 mtrs.

In the case of a larger length of level measurement, multiple detectors will be required, and the detectors need to be connected in cascade mode to cover complete level measurement length of the vessel. Sometimes the single nuclear source may not be able to cover the complete level measurement length, so multiple nuclear sources may be required. This is determined via Nuclear Source strength calculations.

When multiple detectors are used, the same required to be connected in Master-Slave configurations.

The Master detector aggregates (sums up) the signal received from all slave detectors and the output of the master detector corresponds to the total level measurement range of the vessel. The master output is connected to Control System (e.g. DCS) which may be 4-20 mA or serial signal.  A detector located either at Top or at Bottom can be configured as Master Detector based on manufacturer recommendations.

The example shown in the article has master at the bottom.

Single Source – Multiple Detectors
In the below configuration, the nuclear source is single and there are two detectors that cover the level measurement range. Hence there is only one master and one slave detector required.


Multiple Source – Multiple Detectors
In the below configuration, two no’s nuclear source and four numbers of detectors are required to cover the whole level measurement range. Hence there will be one master and three slave detectors.
The master detectors have the limitation of maximum no of slave detectors connected (which varies for each supplier); hence we may have to use more than one master detector.

In such cases, both master detectors outputs are connected to a summator device (which may be located at Field or it can be remote) and total output is connected to the DCS system (Below Fig).
Wiring of master and Slave detectors
The typical wiring diagram of multiple detectors is shown below. Each detector generally has cascade input, cascade output, cascade ground, and HART output capability. However when detectors are wired in master-slave configurations, then cascade output of slave is connected to cascade input of other slaves.

The master detector 4 -20 mA output is connected to DCS system which will correspond to total level measurement range.



In certain cases, the current output (4 ~ 20mA) of each detector is also taken to DCS system and the level measurements are mapped in DCS system to arrive at total level measurement (Below Fig 6).

Article by :
Nilima singh
Instrumentation and control Engineer
13 year experience in Detail engineering
Worked on various Refinery, Oil & Gas, Petrochemical and chemical projects

Labels:

Comments

Post a Comment

Popular posts from this blog

What is a Torbar? – Averaging Pitot Tubes

 The Torbar is employed for flow measurement of liquids, gases, or steam in circular, square, or rectangular section ducts for large flow rates. The Torbar is an insertion type multi-port self-averaging primary sensor for flow measurement. Torbar TORBAR is a set of Pitot tubes mounted on a bar across the pipeline with no moving parts. An averaging Pitot tube is a technology, while TORBAR is a manufacturing brand name. There are several brands available in the market with VERABAR, ANNUBAR, etc. Averaging Pitot Tube Principle Purpose Averaging Pitot tube can be employed when the average velocity of the flow profile, rather than the velocity in a specific point in the cross-section is desired. Averaging Pitot Tubes Principle It measures the differential pressure between the static pressure tap and the tap of full pressure of a stream. Thus such magnitude of differential pressure is directly proportional to the square of the flow rate. Working The TORBAR is designed in such a way that ...
7 comments
Read more

Ferrules and Cross Ferruling

 Ferrules are identification labels provided for every wire terminations in an instrument, equipment, or electrical/instrumentation control panels. These tube-shaped sleeves can be inserted easily on each individual wire in a multi-core cable. In earlier days fixed digits/letters are used as ferrules, but now Instrumentation engineers/technicians prints out desired ferrules by using a ferrule printing machine. Typical Ferrule The numbers/ letters on the ferrules will be given as per the approved electrical hook up or loop diagrams. This helps technicians to easily identify a particular loop/wiring from a series of terminal blocks and to troubleshoot the desired terminal connection. Separate numbers on the ferrules distinguish the positive and negative polarities of wires, thus ensure the polarity protection of the instrument. Cross Ferruling  As a wire is connected on its both ends, it is quite useful to use a cross reference method for wire identification. Unlike normal ferru...
1 comment
Read more

Thermowell Insertion and Immersion Length

 The thermowell is the industrial housing for temperature elements like RTD or thermocouple or temperature gauges. Thermowell is directly exposed to process fluid/media. Inside the thermowell, element/gauge is installed. Thermowell transfers the heat to the temperature element. Depending upon the element type, the fluid temperature can be known. So Thermowell protects the temperature element against harsh conditions and process fluid. It enables removal of the temperature element for replacement, repair, or testing without affecting the process system. Generally, thermowells are provided with all-temperature Elements like RTD or Thermocouple or temperature gauge. A few exceptions would be bearing RTD, skin type thermocouple, air duct thermometer, etc where thermowell is not applicable / required. When the thermowell assembly is inserted into the pipe, it is subjected to vibration. This vibration is caused by vortices to be generated alternately on either side of the thermowell. The...
1 comment
Read more