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.
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 pages.
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.
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).
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 a newbie.
This is the main Schematic Diagram of the
Standard J and K Thermocouple Signal
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
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
This also has a Proportional Current or Voltage
output for a Strip Chart Recorder, Data Logger or to
report to the Supreme SCADA system.