RTD Pt-100 Four Point Alarm - del90001
Here 4052 is used as an analog multiplexer, U3A
TL062 opamp is wired as a 1mA Constant Current
Source. It pumps 1mA into U2 4052
pin 13 X . Depending on BCD code on inputs A,
B of 4052 the current is routed to any one of
the four RTD 100E, whose one end is connected to
X0-X3. The current then flows to GND thru the
Platinum 100E resistance. The Y0-Y3 monitors the mV
developed on RTD in tandem with X0-X3
positions. Like a ganged rotary
switch. The Output mV at Y is the mV of Active
Channel as selected by the BCD of 4029.
See another way 4052 is used to route analog signals
to DPM - Analog
mV Switch for Digital Meters
The BCD is provided by 4029 counter which is clocked
by a 555. U5A cancels out the 100E mV (1mA * 100E)
of a cold RTD and Amplifies the differential mV.
This output of U5A is in proportion with measured
temperature. U5B compares the mV that was obtained
with a preset mV of POT1, which is a
user setting called setpoint. The difference is
amplified by U5B which is saturated by U3B
comparator which adds a little hysteresis too. R7-C2
further dampen and slow the response. This finally
drives Q2 to provide a Logic Signal indicating if
temperature is below or above setpoint.
To view the circuit below, Click the Link of PNG
or PDF and view the Circuit, PNG can be Scrolled
with Drag-Drop Left-Click-Mouse and you
could use the PDF to take a paper print for
reference only.
|
PNG-Schematic
PDF-Circuit
|
RTD
Pt-100
Four Point Alarm - del90001 |
|
Below
is a Preview Image Linked to the Larger Circuit
|
It is important to understand process control theory
and the material technologies that go into these
sensors too.
Here is a instrument i used to make in a similar
need - Multizone
Process Scanner
Four points in a Closed Loop Temperature Control
System is Monitored and a Alarm set to go off when
the temperature goes beyond the set limit.
|