Which aspects are to be considered when selecting the switching frequency (C0018)?

When setting the switching frequency a compromise between low noise emission and low drive system (drive controller and motor) stressing is to be found.

The increase of the switching frequency results in a:

• reduced noise development

• enlargement of the switching losses of the semi power conductors (IGBT) => drive controller is heated more intensively

• increasing of the leakage currents (number of pulses)

• reduction of the rated output power of the drive controller

• reduction of the motor current's harmonic wave content => Reduction of the motor temperature

The reduction of the switching frequency results in a:

• stronger noise development => human beings notice this more intensively

• reduction of the switching losses of the semi power conductors (IGBT) => drive controller is heated to a lesser extent

• reduction of the leakage currents => more favourable behaviour regarding bearing currents

• increasing of the motor temperature

• increasing of the motor current harmonic wave content

Basically, the switching frequency/maximum output frequence ratio should not fall below the value of approx. 25:1 (e. g. switching frequency = 8 kHz and a maximum output frequency of 320 Hz). If sine filters or sine interference filters are used, the minimum required switching frequency of 4 kHz (in case of sine filters) or 6 kHz (in case of sine interference filters) is to be considered. Due to resonance frequency if values fall below this minimum frequency, this can lead to a short circuit at the output of the drive controller.

If earth-leakage-circuit-breakers are used, their releasing characteristic can be reduced (frequency response) due to an increased switching frequency, so that it will become less sensitive to the occurring leakage currents

Can the motor voltage and the motor current (at the output of the drive controller) be measured correctly by means of a digital multimeter?

a) Motor voltage:
No, the motor voltage cannot be measured correctly by means of a digital multimeter, as the drive controller presents a pulse-width modulating voltage of the DC bus. Due to technical reasons the digital multimeter is not able to detect the effective value. For measuring the effective value only a moving iron instrument is suitable. The drive controller also presents at code C0052 the effective value of the voltage between the motor phases.

b) Motor current:
Yes, the effective value of the motor current can be measured by means of a digital multimeter (True-RMS), as the frequency inverter shows a sinusoidal current.  The frequency inverter also presents at code C0054 the effective value of the motor current.

 

Can the motor voltage and the motor current be measured correctly by means of a drive controller

a) Motor voltage:
Yes, the effective value of the motor voltage can be measured by means of a drive controller (code C0052).

As an external instrument for measuring the motor voltage at the inverter's output we recommend a moving iron instrument.

b) Motor current:
Yes, the effective value of the motor current can be measured by means of a drive controller (code C0054).

As an external instrument for measuring the motor current we recommend a moving iron instrument or a digital multimeter (True-RMS).

Can the motor voltage and the motor current (at the output of the drive controller) be measured correctly by means of a moving coil instrument

a) Motor voltage:
No. The drive controller presents a pulse-width modulating voltage, which leads to an incorrect display when a moving coil instrument is used. Due to technical reasons the moving coil instrument is not able to detect the effective value. For measuring the effective value only a moving iron instrument is suitable. The drive controller also presents at code C0052 the effective value of the voltage between the motor phases.  

b) Motor current:
No, the motor current cannot be measured correctly by means of a moving coil instrument, as due to technical reasons there is a measuring error. For measuring the effective value a moving iron instrument or a digital multimeter (True-RMS) is suitable.  The drive controller also presents at code C0054 the effective value of the motor current.

How can the motor temperature of group drives be monitored?

Lenze inverters have only one input to the motor-temperature monitoring. If you want to monitor the temperature of e. g. 2 motors, there are two different possibilities:
1. Series connection of the motor-temperature monitoring (thermal contact or PTC) at the terminals T1 and T2.
2. Connect the motor-temperature monitoring (thermal contact or PTC) of motor 1 to the terminals T1 and T2. Connect the motor-temperature monitoring  (thermal contact or PTC) of motor 2 to the terminals 20 (+24 V DC) and e. g. E1 (digital input E1) and link the digital input E1 with the signal TRIP-SET.
In case of type 1 the error message does not give information about which motor has switched off with overtemperature. In case of type 2 this information can be seen from the error message (e. g. OH3 trip for motor 1 or EEr trip for motor 2).

Why can an inverter supply a higher rated current, if selection = 120 %?

The possibility includes some restrictions compared to selection = 150 %:
1. The upper range of the mains voltage has no limit.
2. The chopper frequency is limited.
3. Additional mains chokes / mains filters are necessary to reduce the mains current.
4. The maximum ambient temperature is limited.

In what way does the output power drive controller of 3-phase-power supply change, if power supply is 2 poles (1 pole)?

•    The connectable motor power (motor current) is reduced to ca. 55 % of the drive controller's rated power

•    You always have to use the assigned mains choke (1 phase mains choke is sufficient).

•    The mains current is ca. 110 % of the original output rated current

The 2 phase power supply is not authorized in case of increased rated power                      (max = 120 % IN).

Is it possible to connect a two-phase motor to a frequency inverter?

A two-phase motor can be connected to an inverter without any restrictions. It must be ensured, however, that the rated output current does not change, this means, the extractable apparent power must be reduced by the concatenation factor 1.73.

Note: The input apparent power decreases proportionally, making mains chokes / mains filters unnecessary.

Which addresses do the inputs/outputs of the S7-200 expansion modules receive?

Inputs and outputs are always addressed in an 8-bit grid from x.0 to x.7, even if there are not in actual fact so many real connections available.

Digital inputs and outputs of a CPU have fixed addresses that always begin with I0.0 or Q0.0. Depending on the number of real connections available the addresses are assigned in order (e.g. I0.0 to I0.7 and I1.0 to I1.7 etc.).

The sample CPU in Fig. 1 has 14 inputs, i.e. inputs I0.0 to I0.7 and I1.0 to I1.5 are available. Inputs I1.6 and I1.7 are not there physically, but are still addressed to complete the pattern. However, these "placeholders" cannot be used by the program nor can they be assigned to any successive expansion module.

Fig. 1

Digital inputs of expansion modules are handled in the same way. However, compared with the CPU they have no fixed addresses, but are added to the (real and virtual) inputs available on the left of the module.

Fig. 2

If an expansion module is integrated between two existing modules, all the addresses to the right of the new module change. Fig. 3 shows this sort of change of configuration.

Fig. 3

Analog inputs and outputs are always assigned in pairs and are always addressed with even numbers (AIW0, AIW2 and AQW0, AQW2 etc.). If there is only one real connection on a module, the second is addressed but not used.

Fig. 4

Detailed information on this topic is available in the paragraph entitled "Accessing the Data of the S7-200" in the chapter entitled "PLC Concepts" of the S7-200 System Manual, order number 6ES7298-8FA24-8AH0

Why do you get an error message when program downloading in various S7-200 CPUs of the first generation via S7-200 USB/PPI and RS-232/ PPI Multi Master cable?

When you attempt to download programs in various CPUs of the first generation (S7-21x), you get the following system message: "The CPU does not support this function".
This message occurs when using the S7-200 RS-232/ PPI Multi Master cable (6ES7 901-3CB30-0XA0) or the S7-200 USB/ PPI Multi Master cable (6ES7 901-3DB30-0XA0) together with older versions of S7-21x CPU.

The USB and PC/ PPI Multi Master cable cannot be used with all S7-200 CPUs of the first generation. These communication cables only work with CPUs 212 and 214, release 1.10 or higher, and all CPUs 215 and 216.
CPUs of the 212 and 214 series of releases less than 1.10 do not support the communications protocol required for downloading into the CPU.

The RS-232/ PPI Multi Master cable (with 8 DIP switches) also works with CPUs of the first generation if DIP switch number 5 is set to PPI/freeport ("0"). To accept the change the cable has to be de-energized by switching the S7-CPU 200 off and then on again, or by removing the cable from the S7-CPU 200 and then plugging it in again.

How do I implement the feature of a three step controller with PID Loop in a S7-200?

This entry contains a description of the three step controllers and its configuration in STEP 7 Micro/WIN by means of the supplied blocks as STEP 7 Micro/WIN library.

Example of a Three Step Controller : Water Level 

Fig. 1: Example Water Level 

The  control variable of this  loop is the water level in the tank (current value). The water level is measured by a sensor and supplied to the PID loop . Depending on which setpoint of the water level is given, the electrically adjustable valve must be activated by the motor. The valve can only be opened or closed slowly by the motor. The output of the controller delivers the manipulated variable of the change of the valve position.

Because of the inertness of the valve motor, the given manipulated variable is not directly adjusted at the valve. Thus, the current valve position is determined and compared with output value of the controller.

There are two possibilities to determine the current position of the valve: determination of the valve position via an analog input word, or estimating the valve position by means of the data of the valve motor. If the comparison value (given to the current valve position) is within a tolerance, the valve position is not readjusted. If the deviation between current valve position and the value, given by the controller, is beyond the tolerance, the position of the valves is readjusted until the current value lies inside the tolerance range of the controller value (triggering of the digital outputs "Open valve", or "Close valve"). 

If the valve already is in end position, the end switches will be activated (setting of digital inputs: "Open valve" or "Valve closed") and another triggering of the valve motor is prevented.

The three step controller  with PID loop can be implemented as a program in the S7-200. All necessary blocks (STEP 7-Micro/WIN library as download) and information you can find in this Entry.

Configuration with STEP 7-Micro/WIN Generating the PID Controller  with Micro/WIN V3.2

• Open or generate a STEP 7 Micro/WIN project.

• Start dialog "Extras > Operation Wizard..." .

• Choose "PID Loop" to configure the operation mode of a PID loop .

• If you continue with "next", you will be asked to compile your project and to switch on the symbolic addressing. Confirm the dialog with "Yes".

• In the next step you decide which PID loop  you want to configure. Default setting is configuration "0".

• Confirm the setting with "next".

• In the popped up window you can now define several parameters of the loop. This requires the scaling of the setpoint value and the specification of the controlling element (gain, sample time, integral time and derivative time).

• Apply parameters with "next".

• Next you determine the current value of the process variable and the manipulated variable in the loop. The actual value is a process variable (e. g. analog reading of the water level), which must be stated as input parameter on the PID loop  in the subprogram. Indicate how the process variable is to be scaled. The manipulated variable is the output parameter of the  loop. In order to scale the manipulated variable a digital or analog output type is available. For the three stepcontrol  you use the analog output. Confirm your entries with "next".

• In the next step you can set alarm limits. The example was done without alarm limits. Via "next" you get to the next dialog.

• The operation PID uses a 36 Byte long parameter table in the memory locations and saves the parameters for the PID loop   therein. The PID calculation requires an area to save intermediate results. Enter a byte address in the variable memory area, at which this area for the calculation should begin. Subsequently follow the wizard with "next".

• The wizard assigns preset names to the subprogramm for initialisation and to the interrupt program.

• "next" and "Finish" generate program parts with the set changes, insert then into the project and finish the assistant.

Inserting the Generated  Loop in STEP 7 Micro/WIN
Into your program insert a call of the sub program PID0_INIT. The parameter "PV_I" is linked to the current value of the loop (e. g. analog input value AEW0). At parameter setpoint_R the setpoint is set (range 0...100). The output parameter "Output" is the manipulated variable.

Fig. 2: Call PID_INIT

Implementation of a Three Step  Loop
For the implementation of the three step loop you use the STEP 7 Micro/WIN library, which is availabe for download at the end of this entry. The library contains three subprograms "PID loop_3Step", "PID loop_3Step_NFB" and "Scale_I_to_R". 
The subprogram "PID loop_3Step" and "PID loop_3Step_NFB" implement the principle of a three point controller. In case of "PID loop_3Step" the current position of the actuator (position of the valves) is read via an analog input and is used as input on "PID loop_3Step" after a scaling with "Scale_I_to_R". 

The subprogram "PID loop_3Step_NFB" works with an estimated value of the current valve position. This subprogram is required for all actuators without feed-back (NFB = No-FeedBack). The estimated value depends on the valve motor and on its response time, which must be stated as input parameter for the calculation.

Subprograms "PID_3Step" and "Scale_I_to_R"
With the subprogram "Scale_I_to_R" you can scale an integer to a real. As input parameters you state the integer, its range and the range of the real. Then the subprogram returns the standardized value of the real. 

Use of the "Scale_I_to_R" with the three step  loop
The subprogram "Scale_I_to_R" is required in order to convert the analog input value (range: 0...32000), which displays the current position of the valve, into a real (range 0.0...1.0). The standardized real value is needed as input parameter on the "PID _3Step".

Fig. 3: Scale_I_to_R 

Inserting the Subprogramm "PID _3Step"

Parameters of the subprogram "PID _3Step":

• EN: activating the block with one input or SM0.0

• PID _OUT: calculated standardized manipulated variable of PID loop  block (see data block: VDx  // Calculated  Loop Output)

• MTR_Pos: current standardized valve position (output of "Scale_I_to_R")

• ThrOn: tolerance for the deviation of the manipulated variable (output PID loop) from the measured manipulated variable, in 0.0 to 1.0

• Up_Limit: end switch of the valve: valve opened

• Dn_Limit: end switch of the valve: valve closed

• Up: signal to activate the motor: open valve

• Down: signal to activate the motor: close valve

Fig. 4: PID_3Step

Subprogramm "PID_3Step_NFB"
This subprogram is required for actuators without feed-back (NFB = No-FeedBack).

Parameters of the subprogram:

• PID_OUT: calculated standardized manipulated variable of the PID loop block (see data block: VDx  // Calculated  Output)

• MTR_TM: time the motor needs to change the valve from open to close (in secs.)

• ThrOn: tolerance for the deviation of the manipulated variable (PID loop  output) from the estimated manipulated variable ("PID loop_3Step_NFB") range 0.0 bis 1.0

• En_Limit: allows a correction of the estimated valve position, if the end switch has not been reached yet.
  Example: if the estimated value is 100%, normally the output "Open" was to be reset. Through this function the estimated manipulated variable will be changed to 98% in order to reach the end position really.

• Up_Limit: end switch of the valve: valve opened; in case of valves without end switch and integrated shut-down this input must be connected with "0" signal (SM0.0, NOT).

• Dn_Limit: end switch of the valve: valve closed; with valves without end switch and integrated shut-down this input must be connected with "0" signal (SM0.0, NOT).

• Pulse_TM: minimal impuls time (in 0,1 sec.) for the motor: below this time the valve would not move because of its inertia.

• Break_TM: minimal shut down time/ switch over time (in 0,1 sec.) of the motor: the motor must stop first before it is allowed to move into the other direction.

• Workspace: temporary double word area of the subprogram

• MTR_Sim: estimated value of the current valve position (standardized: 0.0-1.0)

• Up: signal to activate the motor: open valve

• Down: signal to activate the motor: close valve

Fig. 5: PID_3Step_NFB

STEP 7 Micro/WIN  Library as Archive File:
Copy the file "PID_3Step.exe" into a separate directory and then start it via a double click. The STEP 7 Micro/WIN library will be unpacked. Then you can integrate the library, that can be used as of STEP 7 Micro/WIN Version 3.2.4.27, into your S7-200 project.

 How can I connect a TD-200 to the S7-200 interface and use the PC/PPI cable at the same time?

If you want to connect your S7-200 to a TD-200 and the PC at the same time, then the configuration must look like this:



Fig. 1: Configuration

You need an adapter to connect the TD-200. A PROFIBUS with two connectors (including PC connection socket) assumes this function. You connect one side of the cable to the S7-200. You then plug the PC/PPI cable to this connector side. You connect the other side of the PROFIBUS cable to your TD-200. Switch on the terminator on both connectors.

You need the following components for this configuration:

Table 1: Components required

Please note that the PC/PPI cable has to be plugged directly into the PG interface of the PROFIBUS connector. Only in this connection setup is the PC/PPI cable supplied with the necessary power from the CPU.

The power supply for the TD-200 must be separate, because the power supply cannot be via the PROFIBUS cable. Here, you can use the DC sensor power supply of the SIMATIC S7-200 or the power supply unit for the TD-200. To connect the power supply on the TD-200 please use the connector supplied or the cable supplied for the TD-200 power supply.

Adjusting the PPI Multi master mode:
Start STEP 7 Micro/WIN V3 and open the communication window. Open the properties dialog for the PC/PPI cable and activate the multi-master mode under the "PPI" register. Set "USB" as connection in the PG/PC interface, in the properties of the PC/PPI cable, when using the S7-200 USB/PPI Mulit master cable.

Important:
The DIP switch configuration, which needs to be executed at the cable, is dependant on the installed version of STEP 7 - Micro/Win when using the S7-200 RS-232/ PPI Mulit master cable (6ES7 901-3CB30-0XA0). More information can be found under entry-ID: 16532946. The installation of STEP 7 - Micro/Win V3.2 + SP 4 is necessary, if the S7-200 USB/PPI Multi master cable (6ES7 901-3DB30-0XA0) is used.

Note:
The PPI Multi-master mode for the PC/PPI cable can only be selected for the Windows 95, 98, ME, Windows 2000 and Windows XP operating systems. STEP 7 - Micro/WIN is released for Windows XP from version V3.2 + SP3.

If problems arise with the communications, then please check in the Control Panel the settings for the COM port used (the "FIFO" option must be activated) and the size of the receive buffer (must be set the smallest possible value).

How long does the battery module of the S7-200 CPUs last?

The optional battery module of the S7-200 is not used before the high performance capacitor of the CPU is discharged. The battery module is not used for short-term power failures that can be covered by the time for saving data provided by the high performance capacitor. The usually expected utilization duration is 200 days after the high performance capacitor has been discharged.

The maximum life cycle for a battery module is 10 years without utilization.
The data buffering time of the high performance capacitor depends on the CPU. Further information on the CPU-determined buffering times can be found under Entry-ID 431638.

To achieve the full capacity of the high performance capacitor, the CPU must be supplied continously with tension during 24 hours.

Are there are limitations in terms of how you can expand the S7-22x CPU with expansion modules?

Expansion modules can be added to S7-22x CPUs except for the CPU S7-221. If more onboard I/O signals are required in the system, the CPU's onboard I/Os can be expanded by means of additional digital and analog inputs and outputs. There are also various function modules available for the expansion.
The S7-222 CPU can support up to two expansion modules. This is restricted by resources within the CPU. Up to 7 expansion modules can be added to 224 / 226 and 226 XM-type CPUs, regardless of the type of expansion module.

Important:
Only one connecting cable may be used for expansion modules (6ES7 290-6AA20-0XA0) in order to create a multi-line setup.
If you are using a CP 243-2 PLC-interface module, bear in mind that this module occupies two slots.
The maximum number of expansion modules that can be extended depends on the CPU's power balance. Each S7-200 CPU supplies a DC voltage of 5V and 24V DC. The CPU has a 24V DC encoder power supply that delivers a 24V DC to the integrated inputs and to the relay inputs on the expansion modules. If the power requirements for the CPU exceed the internal voltage supply capacity, you can also connect an external 24V DC supply to the inputs and the relay inputs on the expansion modules.
The CPU also has a 5V DC voltage source for the connected expansion modules. If the power requirements of the expansion modules exceed the voltage supply capacity, some of the expansion modules will have to be dispensed with to enable the CPU's energy balance to be complied with.

How do I get access to the program of a password-protected CPU if I do not know the password?

Even if the CPU is furnished with a password protection, the subsequent CPU-Functions can be conducted unlimitedly:

• Reading and writing of user data

• Start, Stopp and Restart of the CPU

• Reading and setting the real-time

Important:
There is no possibility for the user, to read a program of a password-protected CPU with protection level 3 or to modify - without having the knowledge about the password.

If the password entered in the CPU is unknown, a memory reset of the CPU has to be conducted and the program has to be reloaded into the CPU. During the memory reset, the net address, baudrate, realtime and - if existing - the program in the memory submodule are not modified.

1. To implement that, please proceed as follows:

• Select "Target system > memory reset".

• Afterwards, select all three block types to be cleared and confirm it with "OK".

Fig. 1: Selecting blocks to be cleared

• Enter "CLEARPLC" in the dialog window.

An additional possibility to reset the CPU is provided by the program "Wipeout.exe". This program is located on the Installation-CD of STEP7-Micro/WIN or is available in the Internet under Entry-ID: 2123168 .
On the contrary to the reset via STEP7-Micro/WIN, the program "Wipeout.exe" does not only delete the user program, the data block and the configuration information, but also the baudrate is reset to 9,6 kbit/s and the netaddress is reset to address 2. The CPU is reset into the pristine status of supply.

2. Alternatively, the memory submodule can also be plugged with another unprotected program into the CPU. When reswitching the voltage, this program is loaded into the CPU and overwrites the program with the unknown password. Afterwards, the access to the CPU is possible

How can process (read and write) the real-time clock of CPUs in the program?

Using the function "READ_RTC" you have read access to the real-time clock. Under STL the clock is programmed via the TODR VB400 command, whereby the real-time clock data is stored in a table starting at VB400.
Using the function "SET_RTC" you have write access to the real-time clock. Under STL use the TODW VB400 command.

The weekdays are output in code from 1 ( Sunday ) to 7 (Saturday). Using the real-time clock you can start programs in relation to date or time. After an extended power failure or after loss of memory the real-time clock starts with the following parameters:

Which integrated functions do the S7-22x CPUs have?

The following table shows which functions are integrated in which CPUs:

Where can I see the current status of the High Speed Counter?

You want to access the counter value of a High Speed Counter (HSC). For this you specify the address of the High Speed Counter via the memory area (HC) and the number of the counter (e.g. HC0). The current value of a High Speed Counter is write-protected and can only be addressed in double-word format (32 bit).

Addressing examples:

Can the LOGO! switching program be lost following a power failure?

Once the programming function has ended, a switching program is saved on an EEPROM in LOGO! and is power failure-proof.

In the case of all LOGO! versions the basic functions, special functions, time parameters and the elapsed time counter (where applicable) are always retentive.
Current values such as counter statuses can also be stored in the case of a power failure. For this you must activate the "Retentive" option in the function concerned. 

How can you connect a PT100 sensor to the LOGO! Analog expansion module AM2 PT100?

To the LOGO! Analog expansion module AM2 PT100 you can connect sensors with 2-conductor (Fig. 1), 3-conductor (Fig. 2) or 4-conductor (Fig. 3) connections.

In the case of the 2-conductor connection there is no correction of the error caused by the resistance of the measuring circuits. You must build in a jumper between the M1+ and IC1 connections.
 

Fig. 1

In the case of the 3-conductor connection the measuring circuits' resistance is compensated and does not enter the measuring result. For correct measuring results all the conductors must have the same resistance. You achieve this by making sure that the conductors all have the same length and the same cross-section.

 
Fig. 2

In the case of the 4-conductor connection you connect the PT100 in the same way as the 3-conductor connection. The fourth conductor of the PT100 remains open.
 

Fig. 3

Note:
You can use a multimeter to determine the various connections of a PT100 if there is no appropriate data sheet available.
 

Detailed information on the various types of connection is available in section 2.3.2 "Connect inputs of LOGO!" of the LOGO! manual, order number 6ED1050-1AA00-0AE6,