VALTRONICS MODEL 2008SDH-2AP
CARBON DIOXIDE MONITOR
INSTRUCTION MANUAL
Copyright 2017 VTI-Valtronics Inc.
9
VII. TECHNICAL NOTES
1.
How to avoid Ground Loops: As seen in figure 4, you should keep the power supply
circuit and the signal circuits separated. Even though the Power common and the Signal
common are tied together on our printed circuit board, you must run separate wires for
each one and make sure that the Power common wire is a large wire gauge and as short as
possible. The object is to prevent the pulsed power supply current from getting into the
signal path. The power supply current pulses, created by the infrared source turning on
and off every 1.008 seconds, will follow the path of least resistance (represented by R
W1
and R
W2
, the resistance of the wires). The current flowing through the wire resistance
creates a voltage drop (current times resistance) that would appear to be noise if the two
loops were connected together. This is classically called a
ground loop
problem.
2.
EMI (Electro-Magnetic Interference): The infrared detector and its amplifiers are
sensitive to strong magnetic fields that are building and collapsing at 50 Hz and 60 Hz
rates. Examples of this would be devices like fan motors, florescent light fixtures, or AC
solenoids that are within a few centimeters of the 2008. The magnetic field induces a
signal that beats up and down at a period of about 8 to 15 seconds. This can be easily
avoided by keeping the unit away from the sources of the strong fields. If you cannot
avoid being close to an EMI source, then place an earth grounded steel shield between the
EMI source and the 2008.
FIGURE 4
3. See Figure 5. This setup improves
Zero Stability
and
sensor life
.
