VTI Instruments 2008SDH-2AP User manual

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MODEL 2008SDH-2AP
CARBON DIOXIDE MONITOR
Instruction Manual

VALTRONICS MODEL 2008SDH-2AP
CARBON DIOXIDE MONITOR
INSTRUCTION MANUAL
Copyright 2017 VTI-Valtronics Inc. 1
5/22/17
TABLE OF CONTENTS
SECTION TITLE PAGE
I. INTRODUCTION 2
II. DESCRIPTION
A. System 2
B. Power Supply 2
C. Circuit Board 2
Figure 1 - Model 3
D. Gas Cell/Detector 4
Figure 2 - Gas Cell 4
III. INSTALLATION
A. Circuit Board 5
B. Wiring 5
C. Start-up Precaution 5
IV. OPERATION 5
Figure 3 - Diagram 6
V. SERVICING
A. Zero Adjustment 6
B. Span Adjustment 7
VI. SPECIFICATIONS 8
VII. TECHNICAL NOTES 9
Figure 4 – Ground Loops 9
Figure 5 – Using a Filter 10
VIII. ASSISTANCE/TECH SUPPORT 11
IX. WARRANTY 11

VALTRONICS MODEL 2008SDH-2AP
CARBON DIOXIDE MONITOR
INSTRUCTION MANUAL
Copyright 2017 VTI-Valtronics Inc. 2
I. INTRODUCTION
The Model 2008SDH-2AP is a gas detection system designed to determine the carbon
dioxide content of the air for various monitoring applications. It senses and measures carbon
dioxide (full-scale ranges are available from 50% to 100%) and provides a linear output of 0-
1VDC and 4-20mA as a function of carbon dioxide concentration.
The electro-optics gas sensor contains an adjustable, right-angled ⅛” hose barb to provide
gas flow into the optical path, where it is analyzed by NDIR (Non-Dispersive Infrared)
method.
II. DESCRIPTION (See Figure 1)
A. System
The Model 2008SDH-2AP consists of a printed circuit board with the electro-optics gas
sensor. The board contains all the power supply and signal-processing components.
B. Power Supply
The power supply converts the applied 12VDC into various DC voltages to operate the
instrument’s electronics. It consists of diode protection against reverse polarity of the
12VDC input power and solid-state regulators to provide constant voltages for operation
of various electronic circuits.
C. Circuit Board
All circuit components are mounted on a glass-epoxy printed circuit board. This board
includes the gas detection amplifier, electronic components, integrated circuits,
potentiometers, terminal block connector, and fuse.
1. Two multi-turn slotted shaft potentiometers for user-adjustment are:
a) ZERO: to adjust the instrument’s output to read zero voltage in the
absence of carbon dioxide.
b) SPAN: to adjust the sensitivity of the instrument to the required voltage
value to produce a correct reading of a known gas sample.
2. Two additional potentiometers on the board marked “4mA” and “20mA” are
factory set and should not require adjustment.
3. External connections for input power and output for voltage and current are
provided at connector J1. The connector has a row of screw clamp terminals,
which will accept bare stripped wire (#18 awg or smaller).
4. A 1-amp fuse adjacent to J1 for DC input protection.

VALTRONICS MODEL 2008SDH-2AP
CARBON DIOXIDE MONITOR
INSTRUCTION MANUAL
Copyright 2017 VTI-Valtronics Inc. 3
FIGURE 1 (Valtronics Model 2008SDH-2AP)

VALTRONICS MODEL 2008SDH-2AP
CARBON DIOXIDE MONITOR
INSTRUCTION MANUAL
Copyright 2017 VTI-Valtronics Inc. 4
D. Gas Cell / Detector (see Figure 2)
The board-mounted sensor contains a pulsed infrared source, a gas sample cell, optical
filter and detector. The detector provides an electronic signal that is converted into a gas
concentration value (voltage/current output).
Gas detection by the infrared method is based on the principle that most gases absorb
infrared energy at a characteristic frequency. In this instrument, a broadband infrared
source emits energy that is then filtered to produce a narrow range of frequencies
characteristic of the carbon dioxide absorption spectra. The band pass filter is chosen to
match a strong absorption band of carbon dioxide, while avoiding absorption bands from
other gases that may be present. Any carbon dioxide in the gas sample cell selectively
absorbs energy reaching the detector. This change in energy is detected, amplified and
sent to the signal-processing portion of the system.
FIGURE 2 (2008SDH-2AP Gas Cell / Detector)

VALTRONICS MODEL 2008SDH-2AP
CARBON DIOXIDE MONITOR
INSTRUCTION MANUAL
Copyright 2017 VTI-Valtronics Inc. 5
III. INSTALLATION
A. Circuit Board
Place the unit on a flat mounting surface in the area where the presence of carbon dioxide
is to be monitored or controlled. Mount the board on stand-offs using screws through
holes in the corners of the board.
B. Wiring (See Figure 1)
The J1 connections by number are as follows:
1 Positive 12VDC Power Input
2 Ground Common / Return for 12VDC
3 0-1V 0-1VDC Output
4 Ground Common / Return for 4-20mA and 0-1VDC
5 4-20mA 4-20mA Output
C. Start-up Precaution
1. Before applying power and placing the unit into operation, insure that the wiring
is correct.
2. Do not install sensor or interface cable near transformers, fans or power line-
cords.
3. Make sure that the 12VDC power supply (11 to 16VDC) has at least a 0.5 amp
capacity. The unit does not require a regulated supply.
4. A dedicated power supply will also help avoid any ground-loop problems with
recorders or control circuits connected to the signal output of the unit.
5. Separate wires are required for both the Common 4-20mA output and the
Common 0-1V output (if using both).
IV. OPERATION (See Figure 3)
1. Apply 12VDC power to the unit and allow 5 minutes for warm-up.
2. Connect a multimeter to the 0-1V output signal, pins 3 and 4 of J1. With “outside” fresh
air, assumed to contain between 300 to 400 ppm CO2, the reading should be 0.000 volts.
3. Apply CO2 gas through the gas cell – an amount equal to or lower than the “full-scale” of
the unit. Example: if you are checking a 2008SDH-2AP 100% unit flowing 100.00% gas
through the gas cell at a flow rate of about 50ml/min., it should produce a reading of
1.00V ± .050. 50.00% gas should produce a reading of 0.5V ± .025.
4. If the readings are off, refer to Section V (SERVICING) for instructions on how to re-
calibrate the unit.

VALTRONICS MODEL 2008SDH-2AP
CARBON DIOXIDE MONITOR
INSTRUCTION MANUAL
Copyright 2017 VTI-Valtronics Inc. 6
FIGURE 3
V. SERVICING
A. Zero Adjustment
If the accuracy of the unit is in doubt, “zero-check” it by using a cylinder of Nitrogen or
CO2-free air.
1. Remove protective cap from the top of the nitrogen cylinder. Push and thread
pressure regulator valve onto cylinder outlet. Nitrogen is ZERO gas. Fresh air is
about 0.04% (400ppm) CO2,
2. Connect plastic tubing from the pressure regulator outlet to the flow meter inlet
(bottom connection of flow meter).
3. Connect plastic tubing from the flow meter outlet to the inlet of the gas cell.
4. Before applying power, connect a voltmeter to the 0-1V signal output.
5. Verify that the unit has had at least a 5-minute warm-up before attempting any
adjustments.
6. Make sure the flow meter is in a vertical/upright position. Open the regulator flow
valve slowly while observing the flow meter.
7. Adjust the flow to about 50 ml/min. (ml = cc), or about .1 SCFH (Standard Cubic
Feet per Hour).
8. After 3 minutes of continuous nitrogen flow, the signal output should read 0 VDC
± 10 mV. Perform a zero adjustment if required.
9. Depending on the signal output reading, turn the Fine Zero Adjustment (R11)
clockwise for an upscale adjustment or counter-clockwise for a downscale
adjustment. The process will reset the zero reading.
10.Turn off the regulator flow valve and remove the pressure regulator valve from
the nitrogen cylinder.

VALTRONICS MODEL 2008SDH-2AP
CARBON DIOXIDE MONITOR
INSTRUCTION MANUAL
Copyright 2017 VTI-Valtronics Inc. 7
B. Span Adjustment
Note: It is not normally necessary to adjust the span on the Model 2008SDH-2AP. Once
the span has been properly adjusted at the factory, it does not require adjusting. All that is
normally required is a zero check or adjustment.1
If the span adjustment is in doubt, please observe the following guidelines:
1. Verify the zero set point (reference the previous section).
2. Replace the nitrogen cylinder with a cylinder of the desired concentration, usually
mid or near full-scale, of carbon dioxide.
3. Open the regulator flow valve slowly while observing the flow meter. The flow
meter should read about 50 ml/min.
4. Allow the gas sample to flow through the unit for approximately 60 seconds
before any adjustments are made. Perform a span adjustment if required.
5. Refer to the scale data charts (which can be found on the data/spec sheets on our
website) for the corresponding output voltage that matches the sample gas
concentration:
50% full-scale units: http://www.valtronics.com/assets/2008SD50.PDF;
100% full-scale units: http://www.val-tronics.com/assets/2008S100.PDF)
6. Depending on the signal output reading, turn the Span Adjustment (R22)
clockwise for an up-scale adjustment or counter-clockwise for a downscale
adjustment. This process will reset the span.
7. Turn off the regulator flow valve and remove the pressure regulator from the
cylinder.
This completes the checkout and adjustments procedures.
1NOTE: Gas calibration should be done a minimum of once every (6) six months (at least for ZERO
calibration). If you keep a calibration logbook and record how much zero & span drift occur, you can verify if
the calibration interval is correct. You may find that ZERO calibration every 6 months and SPAN once a year is
sufficient to maintain accuracy.

VALTRONICS MODEL 2008SDH-2AP
CARBON DIOXIDE MONITOR
INSTRUCTION MANUAL
Copyright 2017 VTI-Valtronics Inc. 8
VI. SPECIFICATIONS
•Method: N.D.I.R. (Non-Dispersive Infra-red) Sample-Draw type gas sampling
•Gas Sample Hose Barbs: Designed for ⅛ inch I.D. tubing and a flow rates between 0.05
and 0.3 liters/minute
•Gas: Carbon Dioxide (CO2)
•Available Ranges: 0-50%, 0-100%
•Accuracy: ± 5% of reading from ½ scale to full scale and ± .025V from 0.0 % to ½ scale
•Repeatability: ± 1% of full scale (using the same gas sample and assure zero)
•External Power Source: 12 VDC @ .6A max. (11.0 to 16.0 VDC absolute min/max)
•Power Consumption: Less than 3 watts @ 12.0 VDC (2.4 watts typical/7.2 watts peak)
•Output Signals:
Voltage Output: 0 to 1 volt = 0 to full-scale CO2
Current Output: 4 to 20 mA = 0 to full scale CO2
•Zero Drift at Constant Temperature: Less than 2% of full scale per 24 hours (random,
not cumulative)
•Zero Noise at Constant Temperature: Less than 10 mV peak to peak, measured at V
out during any 20-second period.
•Zero Drift due to Ambient Temperature: Less than 0.5% of full scale per degree
Centigrade
•Operating Temperature Range: 0 to 50ºC (32º to 122ºF)
•Storage Temperature Range: -40º to +70ºC (-40º to +158ºF)
•Operating Humidity Range: 5 to 95% Relative Humidity (non-condensing)
•Weight: Less than 0.5 pounds (0.23 kilograms)
•External Dimensions: 3.9” x 5” x 1.5”

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 RW1
and RW2, 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.