Quartz 4

SSO CO2 Sensor

7 min read

CO2 Sensor - Quick Reference SSO

Device Type: Analog Input - Gas Sensor
Signal: 0-10VDC / 4-20mA output
Power: 24VAC/VDC (powered transmitter)
Version: 1.0 | Date: Dec 2025

DEVICE OVERVIEW

Common Models:

  • Veris CWLSHTA, Telaire T8000 Series, Johnson Controls GMP/GMW, Siemens QPA2000, BAPI BA/CO2

Used For:
Demand control ventilation (DCV), indoor air quality monitoring, occupancy detection, energy savings

Specifications:

  • Range: 0-2000 PPM typical (0-5000 PPM for high-occupancy)
  • Accuracy: ±50 PPM typical
  • Technology: Non-dispersive infrared (NDIR) - most common
  • Output: 0-10VDC or 4-20mA proportional to CO2 level
  • Power: 24VAC or 24VDC, 15-50mA consumption
  • Wire Type: 18AWG minimum, shielded recommended for long runs
  • Wiring: 3-wire (power, common, signal output)

Environment: 32-122°F, 0-95% RH non-condensing (indoor only)

SAFETY - PPE REQUIRED

  • ☑ Safety glasses (ANSI Z87.1)
  • ☑ Work gloves
  • ☑ Hard hat (if overhead work)
  • ☑ Ladder safety equipment (if >6 feet)

HAZARDS

  • ⚠ LADDER WORK - Most common hazard (sensors typically mounted high)
  • ⚠ ELECTRICAL - 24VAC/VDC low voltage (low shock hazard, but always exercise caution)
  • ⚠ CONFINED SPACES - Some mechanical room installations

LOCKOUT/TAGOUT

  • NOT required - low voltage device
  • Notify building occupants if working in occupied space

INSTALLATION CHECKLIST

TOOLS NEEDED

  • Drill + bits
  • Wire strippers (18AWG)
  • Screwdrivers
  • Multimeter (DMM)
  • Level
  • Tape measure
  • Label maker
  • Ladder (appropriate height)

PRE-INSTALL

  • Location per blueprints (typically 4-6 feet above floor)
  • Avoid locations near:
    • Doors or windows (outside air infiltration)
    • Supply diffusers (dilutes reading)
    • Kitchen/break room areas (cooking affects reading)
    • Smoking areas or loading docks
  • Verify sensor range matches application (0-2000 vs 0-5000 PPM)
  • Confirm sensor type matches controller input (0-10V vs 4-20mA)

INSTALL STEPS

  1. Mount sensor:

    • Height: 4-6 feet above floor (breathing zone)
    • Representative location (not corner or dead air space)
    • Use level to ensure horizontal
    • Wall mount or electrical box

  2. Route and terminate wiring:

    • 3-Wire Standard:
      • Red: +24VAC/VDC power
      • Black: Common
      • White/Green: Signal output (0-10V or 4-20mA)
    • Tighten terminals: 7-9 in-lbs
    • Support wire, leave 12” service loop

  3. Label wiring:

    • Example: “RM-201-CO2” or “AHU-1-RA-CO2”
    • Label both ends

POST-INSTALL

  • Sensor mounted securely and level
  • Height 4-6 feet above floor
  • Location representative of space
  • All wires terminated tight
  • Labels applied both ends
  • Work area cleaned
  • Photos taken

EXPECTED READINGS

PRE-POWER (Power OFF)

  • Continuity: Each wire <5 ohms end-to-end
  • Isolation: >10K ohms to ground

POWER-UP

  • Supply Voltage: 24VAC/VDC ±10% (21.6-26.4V)
  • Power Consumption: 15-50mA typical
  • Warm-up Time: 5-30 minutes (NDIR sensors need stabilization)

NORMAL READINGS

CO2 LevelCondition0-10V Output4-20mA Output
400 PPMOutdoor air2.0V7.2mA
600 PPMLow occupancy3.0V9.6mA
800 PPMNormal occupancy4.0V12.0mA
1000 PPMHigh occupancy5.0V14.4mA
1200 PPMVery high occupancy6.0V16.8mA

Typical Indoor Range: 400-1200 PPM
Outdoor Fresh Air: ~400-450 PPM
ASHRAE Max Recommended: 1000 PPM (for comfort)
Code Max (some jurisdictions): 1200 PPM

PROOF OUT TESTS

TEST 1: Warm-Up Period

  • Do: Power sensor and wait 5-30 minutes
  • Expect: Reading stabilizes (initial reading may be high or low)
  • Pass If: Reading stable within 30 minutes

TEST 2: Fresh Air Test

  • Do: Hold sensor near outside air intake or open window
  • Expect: Reading drops to ~400-500 PPM (outdoor air level)
  • Pass If: Reading drops and stabilizes at outdoor level

TEST 3: Breath Test (Occupancy Simulation)

  • Do: Exhale breath directly at sensor from 6-12 inches away for 10 seconds
  • Expect: Reading increases 200-400 PPM within 30-60 seconds
  • Pass If: Reading increases then gradually returns to baseline

TEST 4: Range Test

  • Do: Compare occupied space reading to unoccupied/ventilated reading
  • Expect:
    • Unoccupied with ventilation: 400-600 PPM
    • Occupied space: 600-1200 PPM depending on density
  • Pass If: Readings make sense for conditions

TEST 5: Controller Integration

  • Sensor appears in controller AI list
  • Reading displays in PPM
  • Graphics show live data
  • Controller uses reading for DCV control
  • No faults or errors

TROUBLESHOOTING

NO READING / SENSOR FAULT

  1. Verify supply voltage at sensor: 24VAC/VDC ±10%
  2. Wait 30 minutes for warm-up period
  3. Check all wiring connections tight
  4. Test continuity end-to-end: <5 ohms
  5. Measure output signal: Should be 2-10V or 4-20mA (not 0V or 0mA)
  6. If 0V or 0mA: Sensor failed - replace
  7. If voltage present but no reading: Check controller input config

READING STUCK / NOT CHANGING

  1. Verify sensor has power (LED indicator if equipped)
  2. Wait for warm-up period (30 min)
  3. Perform breath test - should increase reading
  4. Check sensor lens/opening not obstructed or dirty
  5. If still stuck: Replace sensor (NDIR element failed)

READING TOO HIGH (Always >1000 PPM)

  1. Check sensor location:
    • Near kitchen or break room?
    • In dead air space with poor circulation?
    • Too close to occupants?
  2. Verify outdoor air ventilation operating correctly
  3. Compare to portable CO2 meter (calibrated reference)
  4. If consistently high by same offset: Calibrate sensor
  5. If true high reading: Increase ventilation rate

READING TOO LOW (Always <400 PPM)

  1. Check sensor location - too close to OA intake or supply diffuser?
  2. Verify sensor not in high-velocity airstream
  3. Compare to portable CO2 meter
  4. If sensor reads low: Calibrate or replace
  5. Note: Reading below 400 PPM indoors is usually sensor error

ERRATIC / FLUCTUATING READINGS

  1. Check for air currents affecting sensor (supply diffuser too close)
  2. Verify sensor mounted securely (not vibrating)
  3. Check wiring for EMI/RFI interference
  4. Look for moisture in sensor or connections
  5. If persists: Replace sensor

SLOW RESPONSE

  1. Normal: CO2 sensors respond slower than temperature (1-2 min typical)
  2. Check sensor sampling rate (some have adjustable averaging)
  3. Verify sensor not obstructed
  4. If >5 minutes to respond: Sensor may be failing - replace

ESCALATION - COMPLETE BEFORE CALLING

PRE-ESCALATION CHECKLIST

  • Verified supply voltage at sensor (24V ±10%)
  • Waited 30+ minutes for warm-up period
  • Verified all wiring connections
  • Performed breath test (reading should increase)
  • Compared to portable CO2 meter (if available)
  • Checked sensor location (away from influences)
  • Documented readings over 30+ minute period
  • Taken photos of installation and location

PROVIDE THIS INFO

  • Sensor: [Mfg / Model / Range / Location]
  • Supply Voltage: _____ VAC/VDC
  • Output Signal: 0-10V or 4-20mA
  • Current Reading: _____ PPM
  • Reference Reading: _____ PPM (if available)
  • Space Occupancy: Occupied / Unoccupied / # people
  • Ventilation Status: OA damper position ____ %
  • Symptoms: [Stuck, erratic, high, low, no reading]
  • Response to Breath Test: [Increased / No change]
  • Steps Taken: [Troubleshooting completed]

CONTACTS

  • Field Specialist: [Phone]
  • Programmer: [Phone] (if DCV sequence issue)
  • Project Manager: [Phone]
  • Dispatch: [Phone]

CALIBRATION

When Needed:

  • Annual calibration recommended (NDIR sensors drift over time)
  • After sensor replacement
  • If reading consistently off by >100 PPM

Methods:

OPTION A: Fresh Air Calibration (Simple)

  1. Expose sensor to outdoor air for 20+ minutes
  2. Outdoor air should read 400-450 PPM
  3. Adjust sensor calibration to 400 PPM (if adjustable)
  4. Note: Only accurate if outdoor air is actually ~400 PPM

OPTION B: Zero Gas Calibration (Accurate)

  1. Requires calibration gas (400 PPM CO2 in nitrogen)
  2. Apply calibration gas to sensor per manufacturer procedure
  3. Adjust sensor to match calibration gas concentration
  4. Preferred method - most accurate

OPTION C: Controller Offset (Temporary)

  1. If sensor consistently off by fixed amount (e.g., always reads 100 PPM high)
  2. Apply offset in controller configuration
  3. Not a permanent fix - sensor should be recalibrated or replaced

Acceptable Tolerance: ±50 PPM

Document: Tech name, date, calibration method, before/after readings

COMMON ISSUES & TIPS

✓ Mount height: 4-6 feet (breathing zone) - CO2 heavier than air but well-mixed indoors
✓ Warm-up time: Always allow 30 min minimum after power-up before commissioning
✓ Location critical: Representative location essential - avoid OA intakes and supply diffusers
✓ NDIR technology: Most accurate but requires annual calibration
✓ Range selection: 0-2000 PPM for most spaces, 0-5000 PPM for high-occupancy (auditoriums, gyms)
✓ DCV savings: Typically 10-30% energy savings vs fixed ventilation rate
✓ ASHRAE 62.1: Requires CO2 sensors for DCV in densely occupied spaces
✓ Breath test: Quick field verification - exhaled breath ~40,000 PPM CO2
✓ Outdoor air: ~400-450 PPM baseline (slowly increasing globally ~2 PPM/year)
✓ False high readings: Check for nearby combustion sources, kitchens, smoking
✓ Multi-zone systems: One sensor per zone typical, or duct-mounted in return air

Document ID: SSO-CO2-001
Revision: 1.0
Next Review: Dec 2026

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