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) or AM1 to AM16 (if 0BA7) AN1 to AN32 (if 0BA7) AQ1 and AQ2 SAQ1 to SAQ16 (if 0BA7) The block number of a function with analog output
Parameter	A: Gain Range of values: -10.00 to +10.00 B: Zero offset Range of values: -10,000 to +10,000 Threshold 1: Difference value above Aen: on/off threshold Range of values: 0 to 20,000 Threshold 2: Difference value below Aen: on/off threshold Range of values: 0 to 20,000 p: Number of decimals Possible settings: 0, 1, 2, 3 Retentivity set (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:

• Analog comparator: Ax - Ay

• Analog threshold trigger: Ax

• Analog amplifier: Ax

• Analog multiplexer: AQ

• Analog ramp: AQ

• Mathematic instruction: AQ

• PI controller: AQ

• Up/Down counter: Cnt

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

• On-delay: Ta

• Off-delay: Ta

• On-/off-delay: Ta

• Retentive on-delay: Ta

• Wiping relay(pulse output): Ta

• Edge triggered wiping relay: Ta

• Asynchronous pulse generator: Ta

• Stairway light switch: Ta

• Multiple function switch: Ta

• Stopwatch: AQ

• Analog filter: AQ

• Average value: AQ

• Max/Min: AQ

• Thresholder trigger: Fre

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: A: 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.

Special Functions Overview