What is Arrays data structure in PLC?| Array Data type.
Published on May20, 2023 | Category: IntroductionShare this Page:
An array is a data structure that can store multiple values of the same data type under a single variable or single tag. array are useful for large amounts of data complex sets of data. Arrays are useful for storing large amounts of data in a single variable or tag. DINT water_level_pre[12].water_level_pre[12] alloocated space for the 12 element array water_level_pre and the element of array are of DINT data type, these element accessed as water_level_pre[0],water_level_pre[1], water_level_pre[2]....water_level_pre[11].Each element in an array is accessed by an index, which represents the position of the element in the array. The index or subscript of an array always starts at 0.Arrays are easy to implement and use, since most programming languages support them as a built-in type or a library. Arrays have fast access time, since we can access any element in an array by using its index in constant time. Arrays have fixed size, which means they cannot grow or shrink dynamically according to the data needs. We have to allocate enough memory for an array at the time of its creation, and we cannot add more elements than its capacity.
how to declare array data type in plc
in a plc an array is declared by specifying its data type, name of array structure (variable name or tag name) and size of array. For example, `real plc1[100]` declares an array of 100 real values name of array is PLC1. Below is example of studio 5000 array declarations of bool and real data type. In array declarations uses square brackets, the number inside the brackets is the index of the element we want to access.
following are common properties of array data structure required for decalration of arra data type.
- SIZE: size specifying The number of elements that an array can hold. The size of an array is fixed and determined at the time of its creation.
- Data type: data type specifying which type of data store in array. for example if array is bool data type so only bool value are store in an array.
- Name: name of array is variable name of array. name of array used to access element of array.
- Index: The position of an element in an array, starting from zero. An index is used to access or modify an element in an array. for example temperature[12] array have 12 element, so elements of array are temperature[0], temperature[1], temperature[3]....temperature[11].
- Element: element is a value that store in an array at a given index. An element can be of any data type that is compatible with the array type. For example, if we have an array of integers, we can store numbers in it, but not strings, Booleans or real values.
types of array in plc
types of array is depend on plc manufacturer some of the plc support single dimensional array but some plc support multidimensional array. Arrays can be classified based on their dimensions, which refer to the number of indices required to access an element in the array.
- One-dimensional Array:linear collection of data where each element is accessed by using a single index value. For example motor_cmd[30] total number of element is equal to size of array.
- Two-dimensional Array: it is matrix also known as matrix array.it is a tabular representation of data where elements are stored in rows and columns. for example temperature[30,30] so total number of elements = 30 * 30 = 900
- multi-dimension: A multi-dimensional array is an array with multiple dimensions, such as a 2D or 3D array. It is represented as a matrix or a table with rows and columns. for example motot_current[30,30,30] are three dimensional array and total number of element = 30*30*30=2700
One-dimensional Array
Mostly in our plc we use single dimensional array, single dimensional array is linear array and it is a very simple array. Element of one dimensional array are accessed by The index value. Index value starts from 0 and goes up to the size of the array minus one. for example real motor_current[12]. array name is motor_current current so we stored 12 motor current in single variable motor_current. and each elements of this array is accessed as motor_current[index name].index name range from 0 to 11 (size of array-1).
example of array single dimensional array in plc
below is the declaration of array data type in studio 5000. in this example we use single dimensional array bool data type.
example of two dimensional array in plc
in a two dimensional array has two index, index are separated by comma (,) in this example we compare temperature value to previous temperature value of process.
example of three dimensional array in plc
below is the example of three dimensional array in studio 5000 plc. This is program for storing motor current here we use a move instructions to move motot_current[0,0,1] to report_data[0,0,2]. in a three dimensional array have three index separated by comma (,).
example of array in Structured Text
above is the example of array in Structured Text we use if else conditional statement. First example is single dimensional array and second example is two dimensional array example.
Use of array in plc
- store and organize data in a structured manner
- store sequences or lists of instructions or actions
- Performing computations on data
- useful plc to plc communication
- useful plc to HMI communication
- useful plc to HMI communication
- store historical data from sensors or other inputs
- perform mathematical operations on data sets