Input Module - J and K Thermocouple with 4-20 mA
This input module converts J, K Thermocouple and 4-20 mA Inputs
to 0-2V Full Scale. These can be used for any voltage/current
inputs too. The RTD module can be modified more easily for
Voltage inputs. The control output can be On-Off or 4-20
mA/Proportional with another card. The 4-20mA I/O STC1000I is
not complete in documentation.
4-20mA Loop-Powered System
This is a Input Signal Conditioning Card for the Temperature
controller. The voltage levels from sensors are either too low
or need to be translated in level and span. Then for greater
accuracy some linearization methods have to be used for a more
precise reading. This also increases the cost. The circuits here
do no cover the linearization see others in this and my related
The step or segment linearization can be done by transistor,
diode or CMOS switches to accomplish varying attenuation/gain
for stages of the curve or voltage levels. In Microcontroller
systems it can be done by lookup tables or math.
Thermocouple with DMM or DVM
In some older digital systems without a MCU, the A to D drives
the address of an Eprom Array to get a Digital Data for Display,
as a linearized Reading. This Corrected Data was in turn made
into analog using a D/A and then on to a Chart Recorder. This
was a Logic only System of the early days. Microprocessor
systems was expensive, power consuming and use to frighten
people by getting lost in loops or a short nap.(they have fixed
that, make sure you code properly).
This is the main Schematic Diagram of the Standard J and K
Thermocouple Signal Conditioning Module.
The Circuits and Pcb layouts are below. PNG images can be
Viewed, If you want to build it take a paper print using the
PDF copies also below. The PCB Layouts may need to be scaled
to get usable PCBs.
Derivative Modules from Same Card
J-K Proportional Type
This is the same as above with some spare components used for
configuring a proportional controller also with the proportional
card. The documentation is not complete and may not be easy for
4-20mA In-Out Module
- This can be configured as a Current or Voltage Input Module.
The shunts or dividers must be put externally near terminal
block must be 1% MFR Resistors in Series/Parallel. Current
should not heat up R.
The attenuators is also sometimes external, when you have a
voltage like 100V from tacho, damping too. AC Voltages are also
to be rectified and attenuated near terminal block. Zeners for
protection. Then this can be used for AC voltage control for use
in Servo Controls.
This also has a Proportional Current or Voltage output for a
Strip Chart Recorder, Data Logger or to report to the Supreme
PDF Schematics of Modules
PCB Cards of Input Module
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