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Monday, June 15, 2015

RTD PT100 Transmitter and Multiplexer

This is a RTD Pt-100 Transmitter, It can Convert Thermocouple mV or RTD mV to 4-20 mA Current Transmitter. The output is a current source and not a current sink. It goes to a 4-20mA Mux with a common ground. The Circuit RTD-Pt-100-Transmitter.

RTD 3-W Mains Power 4-20 mA Transmitter

This low-cost transmitter was made to send RTD information in a 4-20mA over long distance. The 4-20mA was the input to a Analog-Mux which interfaced to a GE-Fanuc PLC system and a 486 Computer. The Analog Multiplexer Built around CD4051 was was controlled by PLC to get data from numerous channels. This reduced the cost of the System. This is ok when Real-Time Acquisition is not required. The Analog 4-20 to 4-20 Mux-Buffer circuit can be seen at Industrial Process Control Circuits.

RTD Transmitter 4-20 mA

This was done as customer budget could not afford dedicated analog input modules for every channel. There were more than 50 Inputs. The thermal inertia of system did not need a real time or fast correction.

The PNGs of PCB is 600dpi 16 color. It is to be scaled appropriately.

Wednesday, June 10, 2015

Mini RTD Pt100 Three Wire Transmitter

These are the circuits and boards of a Mini Temperature Transmitter for a Platinum hundred ohms temperature Sensor.

The customer wanted a two wire system, this needs low power opamps which were ten times the price. If this transmitter works at 3mA it could have been two wire. Those parts were in short supply and the budget of customer was low. So i made it with regular opamps but three wire. The customer was satisfied as he got a cost effective solution. But now the situation of markets and products are different.

Mini RTD Pt100 Three Wire Transmitter

RTD  Three Wire Transmitter

If you need to transmit the temperature from a high voltage area or toxic environment. You will need to hermetically seal the transmitters, convert the Voltage to frequency, frequency to IR LED flashes or RF. This can be then remotely monitored. Then the transmitter has to be battery-solar operated, low power too. ICL7135 is a simple solution. It has a serial output that can be used to Drive IR Leds. Remotely sense these flashes in a Micro-controller and you have a reading. You may be able to use optic-fibers too. Where volatile liquids are present so that the risks of sparks can be eliminated.

More at Process Control Circuits

This is the same Mini RTD Pt-100 Transmitter but in its case. Encapsulated in epoxy, hermetically sealed against harsh industrial environment. This will work well even near fumes of Ammonia with no corrosion. But not near vapors which can be ignited by sparking as terminals are still open. The side view shows zero and full scale ten turn bourns trimpots heads, for calibration. After cal it can be sealed with RTV compound.

Monday, June 08, 2015

PLC based PID Controller

Below is a Electrical Control Panel, It has a Strip Chart Recorder which is electro-mechanical, It has a PLC Inside. A handheld PLC Programming unit. The computer is showing the Ladder Logic Program. PLC is based on a embedded uC. The DIN Controllers are Analog + Digital circuits. So you see it is a Electrical Control Panel with Electronics and the PLC Ladder Logic means, Software too.

Process Control Application Notes

This is a PID Controller based Control Panel using a PLC from GE Fanuc Automation. The Computer is a 386 40MHz with 40MB HDD.

PID Controller PLC

Electrical Control Panel Wiring

Control panes have many DIN Instruments like Indicators, Controllers and Recorders. They also have in the back end contacters, drives and circuit breakers with orderly wiring and cable management.