Jumat, 14 September 2007

RS232 TO RS 485 INTERFACE FROM PLC GE FANUC

RS232 TO RS 485 INTERFACE

In some application plc will connected with more than 100 m cable or more. This condition will caused the data transfer need buffer to reach the source. In some application we must installing interface to avoid this problem. One of them are RS232 TO RS 485 interface.
With this converter we can connecting module PLC and HMI interface until 1200 m with coaxial cable. A multidrop system of eight drivers and receivers can be configured. The maximum common mode voltage between each additional drop is the RS422 standard of +7 Volts to –7 Volts. The driver output must be capable of ± 2 V minimum into 100 ohms. The driver output impedance must be at least 120 K ohms in the high impedance state. The receiver input resistance is 12 K ohms or greater. Receiver sensitivity is ± 200 millivolt.


Multidrop Connections
In the multidrop configuration, the host device is configured as the master and one or more PLCs are configured as slaves. This method can be used when the maximum
distance between the master and any slave does not exceed 4000 feet (1200 meters). This
figure assumes good quality cables and a moderately noisy environment. A maximum of
8 slaves can be connected using RS422 in a daisy chain or multidrop configuration. The RS422 line must include handshaking and use wire type as specified in the “Cable and Connector Specifications” section. This is electronic diagram RS 232 to RS 485 coverter:





Description of Miniconverter
The Miniconverter consists of an RS422 (SNP) to RS232 Miniconverter, a 6 foot (2 meter) serial extension cable, and a 9pin to 25pinConverter Plug assembly. The 15pin SNP port connector on the Miniconverter plugs directly into the serial port connector on the PLCs. The 9pin RS232 port connector on the Miniconverter connects to an RS232 compatible device. When used with an IBM PCAT, or compatible computer, one end of the extension cable plugs into the Miniconverter’s 9pin serial port connector, the other end plugs into the 9pin serial port of the computer. The Converter plug (supplied with kit) is required to convert the 9pin serial port connector on the Miniconverter to the 25pin serial port connector on the IBM PCXT or PS/2 Personal Computer.

Kamis, 13 September 2007

INPUT ANALOG CONTROL FROM THERMOCOUPLE OPERATION


Block Operation
A Thermocouple Input Block has three isolated pairs of inputs. Transformers isolate
power and optical couplers provide signal isolation.
For each pair of inputs:
1. After filtering, each signal input is sequentially switched into a common amplifier
whose output is applied to a voltage–to–frequency converter. The output signal
frequency of the VFC is applied to a frequency counter via an optical coupler. The
output frequency is counted for a 400 millisecond gate time, which is a common
multiple of all the common line frequency periods. This provides considerable
rejection of line frequency pickups.
2. The multiplexer intersperses other inputs between the two main thermocouple
input times. The other inputs come from the cold junction sensors and from internal
references. The cold junction inputs are measured and stored for later
compensation of the normal thermocouple input measurement errors.
3. To detect and correct for any gain or offset drift in the amplifier or VFC, the block
takes new readings of factory–calibrated internal reference levels during operation.
These new measurements are compared to reference values stored by the block.
4. The processor converts the cold junction temperature value to a voltage as specified
by the NBS monograph for the thermocouple type in use. This voltage is then
added to the thermocouple measurement before converting to thermal units. Since
there may be some small differences between the cold junction temperature
measurement and the actual cold junction temperature, an offset adjustment can be
entered using a Hand–held Monitor. These offsets are due to variances in the
terminal strip assembly and the correction factors are therefore stored in the
Terminal Assembly EEPROM.


Block Measurement Accuracy
The overall accuracy of the block in a given application depends on both:
1. Accurate measurement of the thermocouple millivolt signal.
2. Accurate compensation of the cold junction connections.
The block can measure the input millivolt signal to an accuracy of " 10mV (typical) or "
20mV (maximum). Depending on the thermocouple type used and the temperatures
being measured, measurement accuracy in C or F can be determined.
The output from a thermocouple varies in a non–linear manner as the temperature
being measured changes. Furthermore, each thermocouple type has a unique
characteristic.
The following table may be used as a guide to estimate accuracy in units of degrees. It
lists optimal accuracy for each thermocouple type, without allowing for conditions that
might be encountered in the application, or for the accuracy of the specific thermocouple
being used. For a more accurate estimate, consult the NBS monograph published for the
thermocouple type used in the application, referencing the temperature range to be
measured.
Thermocouple Type Average Sensitivity: mV/C Optimal Accuracy in C




Cold junction compensation can be performed internally by the block itself, or remotely.
The block has a cold junction sensor which is set at the factory to compensate the cold
junction to within " 2C typically. If a more accurate setting is required, this
compensation can be adjusted using a Hand–held Monitor, after the block is installed

CONTROLLING FOOD PROCESSING WITH PLC AND HMI CONTROL SYSTEM

PLC as Popular control in industrial
PLC is most popular module to control process in industry, because they have some advantages : simple to programing, module packaging, easy to improve, least wiring, cimplyfied modification, and other advantages.

The PLC Micro and Nano have various communications options to meet your control needs. Each unit has an RS-232 port that can be used for SNP Slave, Modbus RTU Slave or Serial In/Out commands. The second port on the 23 point and 28 point micro is an RS-485port that supports SNP Slave, SNP Master, Modbus RTU Slave and Serial In/Out commands. Modems can easily be attached to either port. With the Serial I/O commands you can interface to devices such as pagers, intelligent scales, bar code readers and printers. Serial I/O can be used to Serial Port Applications
cause of that PLC used to control almost equipment. with HMI progam, PLC interfaced with human with easy way. HMI and PLC comunicated to monitoring status and controlling.
As a controlling, PLC used analog and digital input or outpu. for exsample analog input used for controlling and monitoring temperature using thermocouple and it's module . Thermocouple sent electronic signal then Thermocontrol sent signal 4-20 mA to PLC. PLC will translate it's signal and convert it into digital signal. MMI will get signal from PLC and translate it ioto Uhman interface. so people can easy control ang monitor Temperature status and control it using PID control system.
Food processing need specific handling and controlling all aof the process. starting from milk reception until packaging product.

dairly processing handbook from Tetra Pack

Pasteurisation teory

pasteurization priciple was founded by Louis Pasteur, where material will get heating effect to sterilized the material. Heating effect usually using steam to transfer energy

Final heating to pasteurisation temperature with hot water, normally of a temperature 2 – 3°C higher than the pasteurisation temperature (D t = 2 –3°C), takes place in the heating section. The hot milk continues to an exter-nal tubular holding cell. After the hold, the temperature of the milk is checked by a sensor in the line. It transmits a continuous signal to the temperature controller in the control panel. The same signal is also transmitted to a recording instrument which records the pasteurisation temperature.

Dairy Processing Handbook/chapter 14 292 Pasteurisation Before the actual cheesemaking begins, the milk usually undergoes pre-treatment designed to create optimum conditions for production. Milk intended for types of cheese which require more than one month for ripening need not nessesarily be pasteurised, but usually is. This implies that cheese milk for types needing a ripening period of at least one month need not be pasteurised. Whey used for fodder must however be pasteurised to prevent it from spreading bovine diseases. However, if the cheese milk is pasteurised it is not necessary to pasteurise the whey separately. Milk intended for original Emmenthal, Parmesan and Grana, some extra hard types of cheese, must not be heated to more than 40°C, to avoid affecting flavour, aroma and whey expulsion. Milk intended for these types of cheese normally comes from selected dairy farms with frequent veteri-nary inspection of the herds. Although cheese made from unpasteurised milk is considered to have a better flavour and aroma, most producers (except makers of the extra hard types) pasteurise the milk because its quality is seldom so dependable that they are willing to take the risk of not pasteurising it.
Pasteurisation must be sufficient to kill bacteria capable of affecting the
quality of the cheese, e.g. Coliforms, which can cause early “blowing” and a
disagreeable taste.

Regular HTST pasteurisation at 72 – 73°C for 15 – 20 seconds is there-fore most commonly applied. However, spore-forming micro-organisms in the spore state survive pasteurisation and can cause serious problems during the ripening process. One example is Clostridium tyrobutyricum, which forms butyric acid and
large volumes of hydrogen gas by fermenting lactic acid. This gas destroys the texture of the cheese completely, not to mention the fact that butyric acid is unsavoury.

More intense heat treatment would reduce that particular risk, but would also seriously impair the general cheesemaking properties of the milk. Other means of reducing thermotolerant bacteria are therefore used. Traditionally, certain chemicals have been added to cheese milk prior to production to prevent “blowing” and development of the unpleasant flavour caused by heat-resistant spore-forming bacteria (principally Clostridium tyrobutyricum). The most commonly used chemical is sodium nitrate
(NaNO 3 ), but at production of Emmenthal cheese, hydrogen peroxide (H 2 O 2 ) is also used. However, as the use of chemicals has been widely criticised, mechanical means of reducing the number of unwanted micro-organisms have been adopted, particularly in countries where the use of chemical inhibitors is banned. Regular HTST pasteurization at 72 – 73°C for 15 – 20 seconds is most commonly applied.

Selasa, 11 September 2007

how to control temperature in Direct steam injection

DSI (Direct Steam Injection) are most popular pasteurization system, it's because small and simple design and process.
to get pasteurization procces in milk powder, only need steam and teflon.
steam directly inject into liquid to get high temperature.
to control value of stean pressure we must instal regulator valve ind it's controlled by computer

as aregular process we must create mmi to comunicate sensor temperature with MMI
with PID system we wil get better automatic stem to control temperature output