Analog watchdog

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

Input Ax is one of the following analog signals:

  • AI1 to AI8 (*)

  • AM1 to AM6 (if 0BA6), AM1 to AM16 (if 0BA7), or AM1 to AM64 (if 0BA8)

  • NAI1 to NAI32 (if 0BA7 or 0BA8)

  • AQ1 and AQ2 (if 0BA7), or AQ1 to AQ8 (if 0BA8)

  • NAQ1 to NAQ16 (if 0BA7 or 0BA8)

  • The block number of a function with analog output

Parameter

Gain

Range of values: -10.00 to 10.00

Offset
Range of values: -10000 to 10000

Threshold 1: Difference value above Aen: on/off threshold
Range of values: 0 to 20000

Threshold 2: Difference value below Aen: on/off threshold
Range of values: 0 to 20000

p: Number of decimals
Possible settings: 0, 1, 2, 3

Retentivity on = the status is retentive in memory.

Output Q

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

* AI1 to AI8: 0 to 10 V corresponds with 0 to 1000 (internal value).

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:

For the 0BA7 and later version devices, you can additionally use the actual values of the following already-programmed functions:

You select the required function by the block number.

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

0BA4:

Gain: Range of values: 0.00 to 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

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