In This chapter we discuss about Siemens S7 PLC'S ( Analog Inputs , Analog Outputs , Signal Modules Status Indicators , and Power Supplies ) devices overview.
Analog Inputs
Chapter -14
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4 channel Analog input signal Module
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- An analog input signal is generated by a sensor that provides voltage or current that can vary within a range such as 0 to 10 volts or 4 to 20 milliamps.
- An analog input signal module converts the current or voltage to a binary value that the CPU stores for use in the user program.
- The number of bits in the binary value is referred to as the channel resolution.
- The more bits the greater the number of values that can be represented.
- The resolution available depends on the module.
- For example, the accompanying graphic shows a signal module with a channel resolution of either 13 bits or 16 bits depending on the module version.
- Temperature measurement is an example of an application that requires special signal processing.
- Two types of sensors commonly used to measure temperature are Thermocouples and Resistance temperature detectors (RTDS).
- A Thermocouples is a Temperature sensor made from two dissimilar metals joined at a point called a junction.
- Thermocouple produces a small voltage that is Temperature dependent.
- An RTD also called a Resistance Thermometer is a Temperature sensor made from a metal such as platinum, nickel, or copper that varies in resistance in a predictable manner as temperature varies.
- There are various types of Thermocouples and RTD'S, and each type has different characteristics that determine its application range.
- Because Thermocouple and RTD signals are different and require special processing some Siemens PLC'S have thermocouple and RTD signal modules.
- However the S7- 1500 PLC analog input signal module shown in the accompany graphic can be used with a variety of analog signals including RTD and thermocouple signals.
Analog Outputs
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| 2 Channel Analog output module |
- When a CPU sends a numerical value to an analog output channel, the analog module converts the value to a voltage or current within the range set up for the output channel.
- The channel is typically connected to an analog output device that is controlling something in a machine or process, such as motor speed, valve position, or temperature.
- PLC analog output signal modules vary in the number of output channels, channel resolution, and output signal types.
- The module shown in the accompanying graphic has two analog output channels.
- These channels can be set up for either the -10 to +10 volts range or the 0 to 20 milliamps range.
- The output resolution is 14 bits for the voltage range and 13 bits for the current range.
Signal Module Status Indicators
- Signal modules have LED status indicators that are useful for system Installation and Troubleshooting.
- For example the accompanying graphic shows two S7-1200 signal modules a combination digital input/output signal module and a combination analog input/output signal module.
- Both modules have a status LED for each channel.
- The digital channel status LED is green and turns on when the input or output is on.
- The analog channel LED is green when the channel has been configured and is active and red when there is a channel error.
- Both modules also have a diagnostic LED that is green when the module is operational and red when the module is defective or non-operational.
Power Supplies
- Multiple system power supply types are typically available for a PLC model to match the system voltage.
- System power supplies also specify a power budget which is the available power that a supply can provide to interconnected modules.
- A load power supply provides power to input and output devices and channel circuits.
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| S7-1500 PLC Load power supply |
- In some cases, the load power supply also provides power to other PLC modules including a system power supply module.
- Because input and output devices vary considerably in terms of their current voltage and power requirements load power supplies come in a variety of types and capabilities.
- For example the accompanying graphic shows a load power supply module for an S7-1500 PLC that mounts on the mounting rail with other modules.
- Siemens also manufactures a range of SITOP power supplies for use with many types of equipment including PLC'S.
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| SITOP Power Supplies |
Chapter 15 we will discuss about ( Distributed I/O , System Configuration, PLC Tags , Monitoring values in CPU ) Topics ...
SIEMENS PLC Class for Beginners
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