Quartz 4

SSO Humidity Sensor

7 min read

Humidity Sensor - Quick Reference SSO

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

DEVICE OVERVIEW

Common Models:

  • Veris CWLSHTA (temp/humid combo), Honeywell H7012/H7080, Johnson Controls HT-6000, Siemens QFM, BAPI BA/RH

Used For:
Humidity control (humidification/dehumidification), indoor air quality, condensation prevention, data centers, museums

Specifications:

  • Range: 0-100% RH (Relative Humidity)
  • Accuracy: ±2-3% RH typical
  • Technology: Capacitive polymer (most common), resistive
  • Output: 0-10VDC or 4-20mA proportional to %RH
  • Power: 24VAC or 24VDC, 10-30mA consumption
  • Wire Type: 18AWG minimum
  • Wiring: 3-wire (power, common, signal output)
  • Often Combined: Many models include temperature sensor (dual output)

Environment: -40 to 140°F, 0-100% RH (condensing OK for most models)

SAFETY - PPE REQUIRED

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

HAZARDS

  • ⚠ LADDER WORK - Typical installation 4-6 feet high
  • ⚠ ELECTRICAL - 24VAC/VDC low voltage (minimal risk)

LOCKOUT/TAGOUT

  • NOT required - low voltage device

INSTALLATION CHECKLIST

TOOLS NEEDED

  • Drill + bits
  • Wire strippers (18AWG)
  • Screwdrivers
  • Multimeter
  • Level, tape measure
  • Label maker

PRE-INSTALL

  • Location per blueprints (typically 4-6 feet above floor)
  • Avoid locations near:
    • Direct water spray or steam sources
    • Air conditioning vents (localized humidity)
    • Windows or exterior walls (condensation)
    • Kitchens, bathrooms, locker rooms (unless monitoring those spaces)
  • Confirm sensor type matches controller input (0-10V vs 4-20mA)
  • For duct sensors: Straight section, away from humidifiers/dehumidifiers

INSTALL STEPS - SPACE SENSOR

  1. Mount sensor:

    • Height: 4-6 feet above floor
    • Representative location (not corner or near window)
    • Use level, wall mount or electrical box

  2. Route and terminate wiring:

    • 3-Wire Standard:
      • Red: +24VAC/VDC
      • Black: Common
      • White/Green: Humidity signal
    • If combo temp/humidity (4-wire or 5-wire):
      • Add additional signal wire for temperature
    • Tighten terminals: 7-9 in-lbs

  3. Label: “RM-201-HUM” or “AHU-1-RA-HUM”

INSTALL STEPS - DUCT SENSOR

  1. Lock out air handler (if drilling duct)
  2. Drill penetration: Similar to temperature sensor (3/4”-1” hole)
  3. Insert probe: Typically 6-12 inches into duct
  4. Seal penetration: High-temp duct sealant
  5. Terminate wiring as above
  6. Restore system

POST-INSTALL

  • Sensor mounted securely and level
  • All wires terminated tight
  • Labels applied
  • Duct penetration sealed (if applicable)
  • 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)
  • Warm-up Time: 1-5 minutes (capacitive sensors)

NORMAL READINGS

Humidity LevelCondition0-10V Output4-20mA Output
20% RHVery dry (winter)2.0V7.2mA
30% RHLow (heating season)3.0V9.6mA
40% RHComfortable low4.0V12.0mA
50% RHIdeal comfort5.0V14.4mA
60% RHComfortable high6.0V16.8mA
70% RHHigh (summer)7.0V19.2mA
80% RHVery high8.0V21.6mA

ASHRAE Comfort Range: 30-60% RH
Typical Indoor (Winter Heating): 20-40% RH
Typical Indoor (Summer Cooling): 40-60% RH
Condensation Risk: >70% RH at cool surfaces
Mold Growth: Sustained >60% RH

PROOF OUT TESTS

TEST 1: Warm-Up Period

  • Do: Power sensor and wait 5 minutes
  • Expect: Reading stabilizes
  • Pass If: Stable within 5 minutes

TEST 2: Breath Test

  • Do: Exhale breath at sensor for 10-20 seconds
  • Expect: Humidity increases 10-30% RH within 30-60 seconds
  • Pass If: Reading increases significantly then returns to baseline

TEST 3: Wet Towel Test (Optional)

  • Do: Place wet towel near sensor (not touching)
  • Expect: Humidity increases over 2-3 minutes
  • Pass If: Reads higher with moisture source present

TEST 4: Range Verification

  • Do: Compare reading to conditions:
    • Winter with heating: 20-40% RH typical
    • Summer with AC: 40-60% RH typical
    • Humid day without AC: 60-80% RH typical
  • Expect: Reading makes sense for current conditions
  • Pass If: Reading reasonable for season and HVAC status

TEST 5: Controller Integration

  • Sensor appears in controller AI list
  • Reading displays in % RH
  • Graphics show live data
  • Controller uses for humidification/dehumidification
  • No faults or errors

TROUBLESHOOTING

NO READING / SENSOR FAULT

  1. Verify supply voltage: 24VAC/VDC ±10%
  2. Wait 5 minutes for warm-up
  3. Check wiring connections tight
  4. Test continuity end-to-end: <5 ohms
  5. Measure output: Should be 0-10V or 4-20mA (not 0V or 0mA)
  6. If 0V or 0mA: Sensor failed - replace

READING STUCK / NOT CHANGING

  1. Verify sensor has power
  2. Wait for warm-up period
  3. Perform breath test - should increase reading
  4. Check sensor element not damaged or contaminated
  5. If still stuck: Replace sensor

READING TOO HIGH (Always >70% RH indoors)

  1. Check sensor location - near moisture source?
  2. Verify building HVAC dehumidification operating
  3. Compare to portable humidity meter
  4. Check for water damage or leaks in area
  5. If sensor consistently high: May need recalibration or replacement

READING TOO LOW (Always <20% RH indoors)

  1. Check sensor location - near supply diffuser?
  2. Verify building humidification operating (winter)
  3. Compare to portable humidity meter
  4. If sensor consistently low: Recalibrate or replace

ERRATIC / FLUCTUATING READINGS

  1. Check for air currents (too close to diffuser)
  2. Verify sensor mounted securely
  3. Check wiring for interference
  4. Look for temperature cycling (humidity changes with temp)
  5. Check sensor element for contamination
  6. If persists: Replace sensor

SLOW RESPONSE

  1. Normal: Humidity sensors respond slower than temperature (2-5 min)
  2. Check sensor not obstructed or covered
  3. For duct sensors: Verify in airstream
  4. If >10 minutes: Sensor may be failing

ESCALATION - COMPLETE BEFORE CALLING

PRE-ESCALATION CHECKLIST

  • Verified supply voltage (24V ±10%)
  • Waited 5+ minutes for warm-up
  • Verified wiring connections
  • Performed breath test
  • Compared to portable humidity meter (if available)
  • Checked sensor location
  • Documented readings over time
  • Taken photos

PROVIDE THIS INFO

  • Sensor: [Mfg / Model / Location]
  • Supply Voltage: _____ VAC/VDC
  • Output Signal: 0-10V or 4-20mA
  • Current Reading: _____ % RH
  • Reference Reading: _____ % RH (if available)
  • Temperature: _____ °F (humidity related to temp)
  • HVAC Status: Heating/Cooling/Humidifying/Dehumidifying
  • Outdoor Conditions: Temp _____ °F, Humid/Dry
  • Symptoms: [Stuck, erratic, high, low, no reading]
  • Response to Breath Test: [Increased / No change]

CONTACTS

  • Field Specialist: [Phone]
  • Programmer: [Phone]
  • Dispatch: [Phone]

CALIBRATION

When Needed:

  • Annual calibration recommended
  • If reading consistently off by >5% RH
  • After sensor replacement

Methods:

OPTION A: Salt Test (Simple, Low Accuracy)

  1. Requires: Table salt, small container, sealed bag
  2. Mix saturated salt solution (pile of salt in water)
  3. Place sensor and salt solution in sealed bag
  4. Wait 8-12 hours for stabilization
  5. Should read 75% RH at room temperature
  6. Adjust if reading significantly different
  7. Note: Only accurate to ±5% RH

OPTION B: Calibrated Humidity Chamber (Accurate)

  1. Requires: Humidity calibration chamber or standard
  2. Place sensor in chamber with known humidity
  3. Wait for stabilization (1-2 hours)
  4. Adjust sensor to match chamber humidity
  5. Test at multiple points (33%, 75% RH typical)
  6. Preferred method - most accurate

OPTION C: Reference Meter Comparison

  1. Place calibrated portable meter next to sensor
  2. Wait 10-15 minutes for both to stabilize
  3. Compare readings
  4. If consistently offset: Apply controller offset or recalibrate sensor

OPTION D: Controller Offset (Temporary)

  1. If sensor consistently off by fixed amount
  2. Apply offset in controller configuration
  3. Not permanent fix - sensor should be recalibrated

Acceptable Tolerance: ±3% RH for most BAS applications

COMMON ISSUES & TIPS

✓ Mount height: 4-6 feet typical - humidity generally well-mixed in conditioned spaces
✓ Warm-up time: Allow 5 min after power-up before commissioning
✓ Location critical: Away from moisture sources (humidifiers, sinks, showers) unless monitoring those
✓ Temperature affects humidity: Warm air holds more moisture - expect changes with temp
✓ Relative humidity: % of moisture air can hold at current temperature (not absolute moisture)
✓ Condensation risk: Occurs when surfaces below dew point (typically >70% RH)
✓ Winter heating: Tends to dry indoor air (20-40% RH common)
✓ Summer cooling: AC removes moisture (40-60% RH typical)
✓ Combo sensors: Many include temperature - verify both signals work correctly
✓ Breath test: Quick verification - exhaled breath ~90-95% RH
✓ Calibration drift: Humidity sensors drift more than temp sensors - annual cal recommended
✓ Contamination: Dust, chemicals, smoke can affect accuracy - clean or replace if contaminated

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

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