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 different.
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
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.
The PNGs of PCB is 600dpi 16 color. It is to be scaled appropriately.
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.
and Connections - Mini 3W 4-20mA transmiter
Wiring of another K Type Transmitter shown here.
Input : Thermocouple - 4 + T/C and 5 - T/C --- Output : 4-20mA DC - 1 + I and 2 - I
Supply : 24V DC - 7 + V and 8 - V --- Unconnected terminals - Floating. 3 and 6
20th Mar 2020
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