Mini RTD Pt-100 Three Wire Transmitter
These are the circuits and boards of a Mini
Temperature Transmitter for a Platinum hundred
ohms temperature Sensor. Has a 4-20mA sink output.
Current Loop can be used for multiple instruments.
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
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.