Quartz 4

SSO Pressure Sensor

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Pressure Sensor (Differential) - Quick Reference SSO

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

DEVICE OVERVIEW

Common Models:

  • Setra 264/265/267, Honeywell ST3000, Dwyer 629/679, Johnson Controls P499, Belimo 22DT

Used For:
Duct static pressure (supply/return), filter status, room pressurization, airflow measurement, building pressure

Specifications:

  • Range: Common ranges:
    • 0-0.5” W.C. (filter status, low static)
    • 0-1” W.C. (duct static, most common)
    • 0-2” W.C. (high static, fans)
    • 0-5” W.C. (high pressure applications)
  • Accuracy: ±1% of full scale typical
  • Output: 0-10VDC or 4-20mA proportional to pressure
  • Power: 24VAC or 24VDC, 20-50mA consumption
  • Wire Type: 18AWG minimum
  • Wiring: 3-wire (power, common, signal) + 2 pressure tubes

Environment: 32-122°F, 0-95% RH non-condensing

SAFETY - PPE REQUIRED

  • ☑ Safety glasses (ANSI Z87.1)
  • ☑ Work gloves
  • ☑ Hard hat (mechanical rooms)
  • ☑ Dust mask (drilling ducts)

HAZARDS

  • ⚠ ROTATING EQUIPMENT - Fans, blowers (LOCKOUT required if accessing)
  • ⚠ SHARP EDGES - Sheet metal ductwork
  • ⚠ PRESSURIZED SYSTEMS - Ductwork under positive pressure
  • ⚠ HOT/COLD SURFACES - Supply ducts near coils

LOCKOUT/TAGOUT

  • Required if accessing fan section: Lock out air handler before installing duct probes
  • NOT required for remote wall-mounted sensors with existing pressure taps

INSTALLATION CHECKLIST

TOOLS NEEDED

  • Drill + bits (1/4” for duct penetrations)
  • Wire strippers (18AWG)
  • Multimeter (DMM)
  • Level
  • Tubing cutter
  • Pressure probe kit
  • Duct sealant
  • Label maker

MATERIALS

  • Pressure tubing (vinyl, 1/4” OD typical)
  • Duct pressure probes (if not pre-installed)
  • Tube fittings for sensor
  • Cable ties
  • Duct sealant

PRE-INSTALL

  • Verify sensor range matches application (0-1” W.C. most common for duct static)
  • Confirm sensor type matches controller input (0-10V vs 4-20mA)
  • Identify high and low pressure tap locations per blueprints
  • For duct sensors: Locate in straight section (3× duct diameter from elbows)

INSTALL STEPS

WALL-MOUNTED SENSOR (Typical Installation):

  1. Mount sensor:

    • Location accessible for service
    • Protected from weather if outdoor
    • Use level to ensure horizontal
    • Near pressure tap locations (minimize tube length)

  2. Install duct pressure probes (if not existing):

    • LOCKOUT air handler first
    • Drill 1/4” holes in duct at marked locations
    • Insert pressure probe through hole
    • Probe orientation: Open end facing upstream (into airflow)
    • Seal around probe with duct sealant
    • For static pressure: One probe in supply duct, one in return (or reference to room)
    • For filter ΔP: One probe upstream of filter, one downstream

  3. Route pressure tubing:

    • Connect tubing to duct probes
    • Route tubing to sensor location
    • Support tubing every 3-4 feet with cable ties
    • Avoid kinks or sharp bends
    • Slope tubing toward sensor (prevents condensation accumulation)
    • Keep tube length <50 feet if possible (shorter = faster response)

  4. Connect tubing to sensor:

    • High pressure port: Connect to upstream probe or higher pressure location
    • Low pressure port: Connect to downstream probe or lower pressure location
    • Push tubing firmly into fittings (click or resistance indicates seated)
    • IMPORTANT: Reversed ports will give negative reading

  5. Route and terminate electrical 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
    • Leave 12” service loop

  6. Label wiring and tubing:

    • Wire label: “AHU-1-STATIC” or “FILTER-DP”
    • Tube labels: “HIGH” and “LOW” at sensor connections
    • Label both ends of wiring

  7. Restore system (if locked out)

POST-INSTALL

  • Sensor mounted securely and level
  • Both pressure probes installed and sealed
  • Tubing connected to correct ports (HIGH/LOW)
  • No kinks or restrictions in tubing
  • Tubing sloped toward sensor
  • All wiring terminated tight
  • Labels applied
  • Work area cleaned
  • Photos taken

EXPECTED READINGS

PRE-POWER (Power OFF)

  • Continuity: Each wire <5 ohms end-to-end
  • Isolation: >10K ohms to ground
  • Pressure Tubing: Blow through tubes to verify not blocked

POWER-UP

  • Supply Voltage: 24VAC/VDC ±10% (21.6-26.4V)
  • Power Consumption: 20-50mA typical
  • Zero Pressure Reading: With no pressure difference, sensor should read 0” W.C. (or very close)

NORMAL READINGS - DUCT STATIC PRESSURE

ApplicationTypical Range0-10V Output (0-1” range)
Supply duct (fan off)0” W.C.0V
Supply duct (fan low speed)0.2-0.4” W.C.2-4V
Supply duct (fan normal)0.5-0.8” W.C.5-8V
Supply duct (fan high speed)0.8-1.2” W.C.8-10V+

ASHRAE Recommendations:

  • Supply duct static: 0.5-1.0” W.C. typical
  • Return duct static: 0.1-0.3” W.C. typical

NORMAL READINGS - FILTER DIFFERENTIAL PRESSURE

Filter ConditionTypical ΔP0-10V Output (0-1” range)
New/clean filter0.05-0.15” W.C.0.5-1.5V
Normal filter0.2-0.4” W.C.2-4V
Dirty filter (replace)0.5-0.8” W.C.5-8V
Severely plugged>1.0” W.C.>10V

Filter Change Threshold: Typically 0.5-1.0” W.C. depending on filter type

NORMAL READINGS - BUILDING PRESSURIZATION

ApplicationTypical Range
Operating rooms (positive pressure)+0.01 to +0.05” W.C.
Isolation rooms (negative pressure)-0.01 to -0.05” W.C.
Labs (negative pressure)-0.02 to -0.10” W.C.
Data centers (slight positive)+0.01 to +0.03” W.C.

PROOF OUT TESTS

TEST 1: Zero Check

  • Do: Disconnect both pressure tubes from sensor (open to atmosphere)
  • Expect: Reading should be 0” W.C. (±0.01”)
  • Pass If: Reads within ±0.01” W.C. of zero
  • If not zero: Some sensors have zero adjustment - calibrate per manual

TEST 2: Tube Orientation Test

  • Do: With system running, note current reading
  • Do: Swap HIGH and LOW tubes at sensor
  • Expect: Reading should reverse sign (positive becomes negative)
  • Pass If: Sign reverses - confirms tubes connected correctly
  • Do: Swap tubes back to correct orientation

TEST 3: Response Test

  • Do: Start/stop fan (or change fan speed)
  • Expect: Reading changes proportionally within 5-10 seconds
  • Pass If: Reading responds to pressure changes

TEST 4: Tube Blockage Test

  • Do: Gently blow into LOW pressure tube (disconnect from sensor first)
  • Expect: Can blow through easily, feel air at duct probe
  • Pass If: No blockage detected
  • Repeat for HIGH pressure tube

TEST 5: Controller Integration

  • Sensor appears in controller AI list
  • Reading displays in inches W.C.
  • Graphics show live data
  • Controller uses reading for fan/damper control
  • No faults or errors

TROUBLESHOOTING

NO READING / ZERO ALL THE TIME

  1. Verify supply voltage at sensor: 24VAC/VDC ±10%
  2. Check output signal: Should be 0-10V or 4-20mA (not fixed at 0V/4mA)
  3. Verify pressure tubing connected to both ports
  4. Blow through tubes to check for blockages
  5. Check duct probes not plugged with dirt/debris
  6. If sensor has power but reads zero with system running: Tubes may be reversed or blocked

READING NEGATIVE (When Should Be Positive)

  1. HIGH and LOW tubes reversed - swap tubes at sensor
  2. Verify duct probe orientation (open end into airflow)
  3. Check that controller input not configured backwards

READING TOO HIGH OR TOO LOW

  1. Verify sensor range matches application:
    • Filter ΔP typically needs 0-1” W.C. or 0-2” W.C. range
    • Duct static typically 0-1” W.C. range
    • High static fans may need 0-2” or 0-5” W.C. range
  2. Check for kinked or restricted tubing
  3. Verify duct probe locations per design (not in turbulent area)
  4. Compare to handheld pressure meter (Magnehelic or digital)
  5. If consistently offset: Calibrate zero point

ERRATIC / FLUCTUATING READING

  1. Check for water condensation in pressure tubing:
    • Disconnect tubes and blow out water
    • Improve tubing slope toward sensor
    • Consider installing drip legs or water traps
  2. Verify duct probes in smooth, straight duct section (not near elbows, dampers)
  3. Check for air leaks in tubing connections
  4. Look for tubing vibration (fan vibration transmitted through tubes)
  5. If persists: Replace sensor (diaphragm may be damaged)

SLOW RESPONSE

  1. Check pressure tubing length (>50 feet = slower response)
  2. Verify tubing not kinked or restricted
  3. Check tubing diameter adequate (1/4” OD typical)
  4. Look for water accumulation in tubes
  5. Note: Some slow response is normal for long tube runs (10-30 seconds)

READING DRIFTS OVER TIME

  1. Temperature compensation issue - verify sensor in stable temp environment
  2. Check zero point calibration
  3. If drifts significantly: Replace sensor (diaphragm aging)

ESCALATION - COMPLETE BEFORE CALLING

PRE-ESCALATION CHECKLIST

  • Verified supply voltage at sensor (24V ±10%)
  • Verified pressure tubes connected to correct ports (HIGH/LOW)
  • Blown through tubes to check for blockages
  • Checked duct probes not plugged with debris
  • Verified sensor range appropriate for application
  • Compared to handheld pressure meter (if available)
  • Checked for water in pressure tubing
  • Documented readings with system on/off
  • Taken photos of installation

PROVIDE THIS INFO

  • Sensor: [Mfg / Model / Range / Location]
  • Application: Duct static / Filter ΔP / Room pressure / Other
  • Supply Voltage: _____ VAC/VDC
  • Output Signal: 0-10V or 4-20mA
  • Current Reading: _____ ” W.C.
  • Expected Reading: _____ ” W.C. (based on application)
  • Handheld Meter Reading: _____ ” W.C. (if available)
  • System Status: Fan on/off, speed ____%
  • Tube Length: _____ feet (HIGH and LOW)
  • Symptoms: [Zero, negative, high, low, erratic, slow]
  • Steps Taken: [Troubleshooting completed]

CONTACTS

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

CALIBRATION

When Needed:

  • After installation (zero check)
  • Annually or if reading drifts
  • After sensor replacement

Zero Calibration:

  1. Disconnect both pressure tubes from sensor (open to atmosphere)
  2. Wait 2 minutes for stabilization
  3. Reading should be 0” W.C. (±0.01”)
  4. If not zero:
    • Some sensors have zero adjustment screw/button
    • Or apply controller offset
  5. Reconnect tubes and retest

Span Calibration (if available on sensor):

  1. Requires calibrated pressure source (hand pump with gauge)
  2. Apply known pressure (e.g., 0.5” W.C. for 0-1” range)
  3. Adjust sensor span to match applied pressure
  4. Note: Most sensors are factory calibrated and don’t require span adjustment

Acceptable Tolerance: ±1% of full scale (0.01” W.C. for 0-1” range)

COMMON ISSUES & TIPS

✓ Tube orientation: HIGH port to upstream probe, LOW port to downstream/reference
✓ Tube length: Keep <50 feet for faster response, slope toward sensor
✓ Water in tubes: Common problem - install drip legs or blow out regularly
✓ Probe location: Straight duct section, avoid turbulent areas near elbows/dampers
✓ Probe orientation: Open end facing into airflow (upstream)
✓ Filter ΔP alarms: Typically set at 0.5-1.0” W.C. for filter change notification
✓ Static pressure control: Used for VFD fan speed control, maintains constant pressure
✓ Building pressure: Critical for healthcare, labs, clean rooms - requires tight tolerance sensors
✓ Negative readings: Usually indicate reversed tubes or wrong probe orientation
✓ Range selection: Match sensor range to application - oversized range reduces accuracy
✓ Magnehelic gauge: Mechanical pressure gauge useful for field verification (no power required)

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

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