# 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 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 --- ## 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