S7-200 PLCs are built very compact and powerful: The SIMATIC S7-200 Micro PLC is fast, communication-capable and highly productive in real-time mode.
The S7-200 Micro PLC from Siemens can be used as either a stand-alone Micro PLC solution or in conjunction with other controllers.S7-200 PLCs are built with two different generations of CPUs. Figure 1 displays different categorized models of S7-200 PLCs based on their CPUs.
Figure 2 illustrates few different models of CPU 21X and 22X PLCs. Thus far, S7-200 is produced with 10 different CPU types.
Figure 2 illustrates 4 typical models of 22 X series – from top left CPU 221, CPU 222, CPU 224 and finally CPU 226
Production of CPU 21X is discontinued, and since CPU 22X and SIPLUSE 22X are physically smaller with higher clock rate compared to 21X, they are the models mostly used in industries nowadays. The former CPUs have some digital I/O ports on board. SIPLUSE 22X models are designed to withstand temperature ranges from 25C to 70C and function in Hydrochloric and Sulphuric chemical environments.
In order to use a PLC to control a process, it must be hardwired to power supply and some field devices. Figures 3 and 4 display how two different models of SIMATIC S7/200 families can be hardwired to input/output devices. As an example, CPU 221 DC/DC/DC is supposed to be energized by a 20.4 to 28.8 VDC power supply, it has 14 DC inputs and 10 DC outputs. See Figure 3.
On the other hand, CPU 222 AC/DC/RLY (means PLC is supposed to be energized by 85-264 VAC mains power source @ 47-63 Hz), it has 8 DC inputs and 6 relay outputs. See Figure 4.
Figure 4 displays I/O, power supply and DC sensor supply section of S7-200 model pictured in Figure 3. In figure 3 there are bunch of LEDs which inform the operator what is the working condition of PLC in use. The meaning of any led is turned on/off is as following Status LEDs:
SF: System Fault, RUN: PLC is executing a program STOP: standby mode.
I/O LEDs: turns on anytime, each input or output port is activated.
TERM SWITCH: (top right): when mode switch is on “RUN”, position, CPU executes the prepared software. CPU “STOPS” execution when switch on stop position. And finally when switch is positioned on “TERM”, PLC operator is ready to choose the PLC’s operating mode.
POT1, POT2: analog potentiometers to control analog sensor settings (top right).
M/L (output DC Sensor Supply) terminals: PLC provides 24 VDC power for input sensors or expansion modules (280 MA).RS232 Port: is used to connect PLC to a PC and download programs.
In Figure 5, under little access door indicated by number “1”, these facilities are located:
Mode selector switch (RUN/STOP), analog adjustment potentiometer(s), and expansion port (for most CPUs). Mode selector switch STOP, TERM, RUN function as it was mentioned for CPU 214.Status LEDs: System Fault, RUN, STOP also functions as explained already.Section indicated by number “2” can accommodate an optional cartridge: EEPROM, Real-time Clock battery.
The “Analog adjustment” can be used to increase or decrease some values related to PLC’s Timer or Counter set values. When the POT is turned around, it does change the numerical analog values related to set values or limits inside the special section located in PLC’s memory.
Optional Cartridge can be used to transfer program from one S7-200 to another S7-200 one. This cartridge is usually an EEPROM type of storage device.For S7-221 and S7-222 there is a real-time clock with battery backup available (can be placed inside of the cartridge socket). The battery provides up to 200 days of data retention time in the event of a power loss. The S7-224 and S7-226 have a real-time clock built in. Another cartridge is available with a battery only.
Figure 6 displays different configuration of SIMATIC S7-200 PLCs.
SIMATIC S7-200 Function modules:
SIMATIC S7-200 has a consistently modular design. In addition to expansion and communication modules, the modular system provides a range of specific expansions for positioning, weighing technology and temperature measurement. Expansion modules contain additional inputs and outputs. These are connected to the base unit using a ribbon connector. Expansion modules usually are installed on the same Rail and usually at the right side of the base unit.
Summarized description of some Available Expansion Modules: Positioning Module EM 253 is a function module for simple positioning tasks (1 axis). It can be connected to stepper motors and servo motors from the Micro Stepper to the high-performance servo drive via a high-frequency pulse input. The EM 253 positioning module is mounted in the same manner as an expansion module and connected to the S7-200 expansion bus via the integrated connection cable. The configuration data are read out of the CPU automatically on connection. The module has the following features:
5 digital inputs for signals from the process, 24 pulse outputs for direct activation of the drive (forwards/backwards or speed/direction), 2 control outputs (DIS; CLR) and 12 status LEDs.
Weighing Module SIWAREX MS is a versatile weighing module for all simple weighing and force measuring tasks. The compact module is easy to install in the SIMATIC S7-200 automation systems. The data for the actual weight can be accessed directly in the SIMATIC CPU without the need for any additional interfaces. Measurement of weight or force with a high resolution of 65000 parts and an accuracy of 0.05 % .Simple adjustment of the scale using the SIWATOOL MS PC program via the RS 232 interface.
Thermocouple Module EM 231 (Analog Module) is a highly accurate temperature sensor using standard thermocouples. Low-level analog signals in the range of ±80 mV can also be detected. The thermocouple module EM 231 can be used with CPU 222, 224 and 226.
4 or 8 analog inputs.
Different measuring ranges: Type J, K, T, E, R, S and N thermocouples; ±80 mV analog signal acquisition Check for open lines Compensation of the cold connection point Temperature scaling: The measured temperature can be specified in °C or °F.
Thermo-resistor Module EM 231 RTD (Analog Module). The thermo-resistor modules EM 231 are a highly accurate temperature sensor using standard resistance temperature detectors. They can be used with CPU 222, 224 and 226. The thermo-resistor module should be installed in locations with low fluctuations in temperature to ensure the highest accuracy and repeatability. Two or four analog inputs for temperature detectors All resistance temperature detectors must be the same type Installation directly to the wall or on DIN Rail. In addition to the mentioned Expansion modules, these modules are also available:
EM 221: for CPU 22X Digital input ~ by this module, one can add max 8 digital inputs to the base unit.
EM 222: Digital output ~ by this module, max 8 outputs can be added to current outputs of the PLC.
EM 223: Digital I/O ~ max of 16 digital I/O could be added to the base unit.
EM 277 Profibus-dp ~ slave module is an intelligent expansion module designed to work with the S7-200 CPUs. As it was mentioned previously, not all S7- 200 PLCs come with the equal capability. For example CPU 221 has 6 INPUTS, 4 OUTPUTS on board but does not accept any expansion unit. Table shown in Figure 7 illustrates which PLCs can be connected to external Expansion units.
Addressing of Digital expansion units:
From table shown in Figure 7, we notice that different CPUs can accept certain number of expansion units. For example CPU 222 can only accept 2 units of EM expansion modules. But up to 7 units of EM expansion modules can be added to CPU 224. Question is how the addressing is going to be done when we connect some I/O (EM units) devices to these PLC base units?
When it comes to addressing I/O terminals located on a PLC unit, manufacture has already defined them how the addressing should be done. The same is true when some digital I/O units are connected to base unit (located on the right side of PLC). Let’s say we have a S7-200 PLC with CPU 224 and two I/O units of EM 223 connected to it and located on the right side of the PLC. According to Figure 8, output terminals start from Q0.0, Q0.1… Q0.4 and Q0.5, Q0.6, Q0.7 & Q1.0 and Q1.1 that gives us total of 10 output terminals which each of these can control a single output device independently.
When it comes to input terminals, our numbering start right off I0.0..I0.7 and I1.0, I1.1 …I0.7 and I1.0, I1.1.. I.5 meaning we have total of 14 input terminals that each of these input terminals can control a single input field device independently. When it comes to EM 223 ~ 6ES7 – 1BF22 – 0CAB0 which has only 4 digital combination of I/O terminal numbering continues right after what it is left from previous one. It continues with Q2.0, Q2.1, Q2.2 and Q2.4 and the same numbering is true for the next module. Port numbering for the next EM module continues with Q2.4, Q2.5 … Q2.7 and then Q3.0, Q3.1..Q3.3 which gives us total of 8 independent inputs and outputs.
To download your PLC programs from a PC you need two more items:
1- PLC to PC programming cable 2- STEP7-Micro/WIN software.
Installation of the “PC Adapter USB” driver and selection of the access point in the PG/PC interface. Requirements: You are using the Win2K or WinXP operating system MicroWin V3.2 SP4 or higher has been installed successfully. You are using “PC Adapter USB” V1.1 or V1.2. The drivers and firmware are on the CD supplied or can be downloaded from the following Entry IDs: V1.1: 19136131 or V1.2: 21226394
Description of SIMATIC STEP 7-Micro/WIN:
STEP7-Micro/WIN is an Engineering package for programming the SIMATIC S7-200 it lets you save time and money in programming. This software package can be handled like a standard Windows application and includes all necessary tools for convenient programming of the SIMATIC S7-200: from the high-performance SIMATIC instruction set to IEC 1131-compliant programming and all the way to trend charts and wizards.
The latest version, STEP7-Micro/WIN 4.0, which is compatible with Windows XP and higher operating systems, offers even more: segmented data memory, improved handling of the program and command structures, diagnostic functions as well as a user-specific LED, error history, runtime edit, and online-download.