The temperature in a pipe is monitored with four RTD Pt-100 Sensors, The type of probe could be Extruder RTD probes with Bayonet or Compression Fitting, Get it from Omega. To keep costs low you can choose small thin film RTD sensors, they will be fast but on rough usage may break.
Source Files Orcad Format
The time taken to measure the temperature at the 4 points will be less than 4 seconds. An optional display of the measured temperature as shown above can be avoided by using a DMM to adjust the setpoint.
The Analog Timer Module can be set from 0- 30 minutes. If out-a remains high even after set time a out-b alarm goes on to sound a buzzer and flash a LED light.
Block Diagram :
It all started with a email from a client like this ……….
“I am looking at an idea for a circuit design; The idea is to sense a temp of 130 degrees and then light an LED and start a timer delay. The delay would be 3 min, after the delay if the temp is still above 130 sound alarm.
With the LED I would like to drive a counter display to show how many times the temp was sensed. I would like powered by 120vac and a 9 volt battery backup for counter circuit. If you can assist please let me know.”
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.
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.