Analog watchdog

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Short description

This special function saves the process variable of an analog input to memory, and sets the output when the output variable exceeds or drops below this stored value plus a configurable offset.

 

Connection

Description

Input En

A positive edge (0 to 1 transition) at input En saves the analog value at input Ax ("Aen") to memory and starts monitoring of the analog range Aen +- Delta.

Input Ax

You apply the analog signal to be monitored at input Ax.

Use the analog inputs AI1...AI8, the analog flags AM1...AM6, the block number of a function with analog output, or the analog outputs AQ1 and AQ2.

0 - 10 V is proportional to 0 - 1000 (internal value).

Parameter

A: Gain
Range of values: +- 10.00

B: Zero offset
Range of values: +- 10,000

Threshold 1: Difference value above Aen: on/off threshold
Range of values: 0 20,000

Threshold 2: Difference value below Aen: on/off threshold
Range of values: 0 – 20,000

p: Number of decimals
Range of values: 0, 1, 2, 3

Output Q

Q is set/reset, depending on the stored analog value and the offset.

Parameters Threshold 1 and Threshold 2

The two threshold parameters Threshold 1 and Threshold 2 can be provided by the actual value of another already-programmed function:

You select the required function by the block number.

The thresholds are represented by the symbol Δ on the LOGO! Basic module and in the timing diagram below.

 

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0BA4:

A: Gain

 Range of values 0.00...10.00

Parameter p (number of decimals)

Parameter p applies only to the display of Aen, Ax, Threshold 1 and Threshold 2 values in a message text.

Timing diagram

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Description of the function

A 0 to 1 transition at input En saves the value of the signal at the analog input Ax. This saved process variable is referred to as "Aen".

Both the analog actual values Ax and Aen are multiplied by the value at parameter A (gain), and parameter B (offset) is then added to the product, as follows:

(Ax * gain) + offset = Actual value Aen, when input En changes from 0 to 1, or

(Ax * gain) + offset = Actual value Ax.

Output Q is set when the signal at input En = 1 and if the actual value at input Ax is out of range of Aen + Threshold 1 / Aen - Threshold 2.

Output Q is reset, when the actual value at input Ax lies within the range of Aen + Threshold 1 / Aen - Threshold 2, or when the signal at input En changes to lo.

Particular characteristics to be noted when configuring

Refer to the help on analog block parameters in the Analog value processing section.

 

Overview