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Showing posts from April, 2009

Software to know Electric Cable size

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This program does electrical cable sizing, based on the most basic electrical laws.If you are planning to do cable sizing for a real installation, check the results and make sure that you comply with all electrical regulations.TheoryFrom Ohms law, the voltage drop in an electrical conductor isV = I Rwhere  I = Current, amps  R = Resistance, OhmsThe electrical resistance can be derived from the properties of the conductor material.R = ρ L / Awhere  ρ = Resistivity, Ω mm2 /m  L = Length, m  A = Cross sectional area, mm2Watch the units in the above equation.The resistance can also be expressed in terms of the material conductivity (ψ) which is just the reciprocal of the resistivity.R = L / (ψ A)Table 1.  Typical material electrical conductivityMaterialConductivity, ψCopper58Aluminium36Mild Steel7.7Combining Ohms law with the resistance expression, we get.V = (I L) / (ψ A)Now, we can define an acceptable voltage drop in a conductor.  I have calculated the voltage drop that was used …

How can you set the time of an S7-300 via Industrial Ethernet?

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Instructions:Generally you have two options for this. You can do this either with a CP343-1 IT or a different CP (e.g.: CP343-1) and use S7 communication or UDP communication.  Here you should always use a CP343-1 IT (6GK7343-1GX20-0XE0) as communications processor, because it sets the time of the CPU via the SIMATIC procedure or via the NTP (Network Time Protocol).   If you don't have a CP343-1 IT (6GK7343-1GX20-0XE0), then proceed as described below:
You need an S7-400 (time synchronized, e.g. via SICLOCK) which as time master provides the time to S7-300 via relevant block calls, e.g. PUT (S7 communication PUT, see point A) or AG_LSEND/AG_LRECV (UDP communication, see point B).Configuration with SICLOCK as time master.
Fig. 01
Example for setting the time in an S7-300 with S7 communicationNo.Procedure1First configure a data block with the structure "DATE_TIME" for reading the CPU basic time in the S7-400.
Fig. 022Read out the basic time of the CPU using SFC1 ("READ…

How can you synchronize CPU clocks with each other?

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Instructions:
If multiple CPUs are linked with each other in a subnetwork, you parameterize the clock of one CPU as the master clock. When parameterizing the CPU you also specify the synchronization interval after which all the clocks in the subnetwork are automatically synchronized with the master clock. You call system function SFC48 "SNC_RTCB" in the CPU with the master CPU. The call synchronizes all the clocks in the subnetwork regardless of the automatic synchronization. If you set a master clock with SFC0 "SET_CLK", all the other clocks in the subnetwork are automatically synchronized with that value.
No.Description1Open the Hardware Configuration in the CPU that you wish to parameterize as master CPU and open the Properties of that CPU.2In the Properties of the CPU you select the "Diagnostics/Clock" tab and set the type of Synchronization Mode and Time Interval as shown in Fig. 01. Then save with OK.
Fig. 013Then save and compile the hardware config…

SCADA File Reference

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