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Entry type: FAQ Entry ID: 105824690, Entry date: 12/08/2014
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What should you watch out for when manually entering energy meter values in SIMATIC powerrate?

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Description
As well as automatically capturing energy values the PRE_SUM / PR3_SUM capture blocks also support the manual input of energy meter values in the WinCC user interface. Please note the following points.

Capture mode of the PRE_SUM / PR3_SUM blocks
Use the PRE_SUM / PR3_SUM capture block in energy meter capture mode.

  • Parameter "INP_SEL = 1" with Integer Counter
  • Parameter "INP_SEL = 2" with Analog Counter

You cannot enable manual input of values in the "Pulse" and "Calculation" capture modes.

Weighting factor for scaling the input value
Just as in automatic operating mode, in the "Manual" mode the "WEIGHT_A" weighting factor set at the call interface of the PRE_SUM / PR3_SUM block is also taken into account for scaling the input value. By default, the system expects input in the input mask in WinCC Runtime of values in the unit "kWh" (see figure below of the "Input"/"Edit" view).
For this you set the weighting factor "WEIGHT_A" to the value "1" (1,000e+000) on the PRE_SUM/PR3_SUM block. With this setting the values you enter in the input mask are interpreted as "kWh".


Fig. 01

Handling of units other than kilowatt hours (kWh)
If the energy meter concerned displays values in a different unit "Wh" or "MWh", for example), then you have the options below for data input.

  • The user must convert the values read into "kWh" before entering them in the input mask.
  • The WEIGHT_A scaling factor on the PRE_SUM / PR3_SUM block is changed accordingly.
    • Wh: Factor: 0.001 (WEIGHT_A := 1,000e-003)
    • MWh: Factor: 1000 (WEIGHT_A := 1,000e-003)

    In this case you must also change the faceplate of the input mask to the new unit scaling.
    A description of this is given in the SIMATIC powerrate manual at this link. (You must change the four parameters V_MAN, V_MAN_L1, …_L2, …_L3 to the required unit scaling - Wh or MWh, for example.)

Note
A special case is the temporary switching from "Auto" to "Manual" during runtime (when there is a brief interruption of the field bus connection, for example). In this case the values read and the WEIGHT_A set on the PRE_SUM / PR3_SUM block must be converted before being entered in the input mask.

Example
The measuring instrument delivers the energy meter value via the field bus connection on the basis of "Wh". However, on the display the energy meter is shown with the "kWh" unit.
Thus, before entering the meter value you must convert it to the expected unit of "Wh".
(For example, read value: "734676.67 kWh" > Input: "734676670 Wh").

For this case the display of the default unit "kWh" in "Input"/"Edit" view does not apply. Ignore the unit for the duration of the temporary manual operating mode.

Remark
This scenario of temporary manual input is not usual in practice because the automatic capturing cycle (15 minutes, for example) generally cannot be realized by manual capturing.

Security information
In order to protect technical infrastructures, systems, machines and networks against cyber threats, it is necessary to implement – and continuously maintain – a holistic, state-of-the-art IT security concept. Siemens’ products and solutions constitute one element of such a concept. For more information about cyber security, please visit
https://www.siemens.com/cybersecurity#Ouraspiration.
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