**Device Type:** Analog Input - Gas Sensor

**Signal:** 0-10VDC / 4-20mA output

**Power:** 24VAC/VDC (powered transmitter)

**Version:** 1.0 | **Date:** Dec 2025

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**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

- **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)

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- ☑ Safety glasses (ANSI Z87.1)

- ☑ Work gloves

- ☑ Hard hat (if overhead work)

- ☑ Ladder safety equipment (if >6 feet)

- ⚠ **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

- [ ] **NOT required** - low voltage device

- [ ] Notify building occupants if working in occupied space

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- Drill + bits

- Wire strippers (18AWG)

- Screwdrivers

- Multimeter (DMM)

- Level

- Tape measure

- Label maker

- Ladder (appropriate height)

- [ ] 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)

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:**

* 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

- [ ] 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

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- **Continuity:** Each wire <5 ohms end-to-end

- **Isolation:** >10K ohms to ground

- **Supply Voltage:** 24VAC/VDC ±10% (21.6-26.4V)

- **Power Consumption:** 15-50mA typical

- **Warm-up Time:** 5-30 minutes (NDIR sensors need stabilization)

| CO2 Level | Condition | 0-10V Output | 4-20mA Output |

| --------- | ------------------- | ------------ | ------------- |

| 400 PPM | Outdoor air | 2.0V | 7.2mA |

| 600 PPM | Low occupancy | 3.0V | 9.6mA |

| 800 PPM | Normal occupancy | 4.0V | 12.0mA |

| 1000 PPM | High occupancy | 5.0V | 14.4mA |

| 1200 PPM | Very high occupancy | 6.0V | 16.8mA |

**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

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- **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

- **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

- **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

- **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

- [ ] Sensor appears in controller AI list

- [ ] Reading displays in PPM

- [ ] Graphics show live data

- [ ] Controller uses reading for DCV control

- [ ] No faults or errors

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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

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)

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

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

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

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

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- [ ] 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

- **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]

- **Field Specialist:** [Phone]

- **Programmer:** [Phone] (if DCV sequence issue)

- **Project Manager:** [Phone]

- **Dispatch:** [Phone]

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**When Needed:**

- Annual calibration recommended (NDIR sensors drift over time)

- After sensor replacement

- If reading consistently off by >100 PPM

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

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

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

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✓ **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

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**Document ID:** SSO-CO2-001

**Revision:** 1.0

**Next Review:** Dec 2026