TSI VelociCalc® 9535/9535-A/9545/9545-A Hot-Wire Anemometer

Overview

The TSI VelociCalc® 9535, 9535-A, 9545, and 9545-A hot-wire anemometers are precision-engineered handheld instruments designed for quantitative airflow characterization in HVAC commissioning, indoor air quality (IAQ) assessment, fume hood validation, and critical environment certification (e.g., ISO 14644, ASHRAE 110, EU GMP Annex 1). These instruments operate on constant-temperature anemometry (CTA) principles: a fine platinum or tungsten wire sensor is electrically heated to a fixed temperature above ambient; convective cooling by moving air alters the wire’s resistance, enabling highly responsive velocity measurement across laminar and turbulent flow regimes. Unlike cup or vane anemometers, hot-wire technology provides superior low-end sensitivity (<0.15 m/s), minimal flow disturbance, and fast response time (<100 ms), making it suitable for duct traverse, grille testing, and laminar airflow verification where spatial resolution and dynamic fidelity are essential.

Key Features

• Simultaneous real-time measurement of air velocity, temperature, and — on 9545/9545-A models — relative humidity (RH), dew point, and wet-bulb temperature
• Three-parameter display with user-selectable units (m/s, ft/min, °C, °F, %RH) and configurable decimal places
• Automatic volumetric flow calculation using user-defined duct or grille dimensions; supports switching between actual and standard conditions (STP: 0°C, 101.325 kPa; NTP: 20°C, 101.325 kPa)
• Two probe configurations: rigid telescoping probe (9535/9545) and articulated, bendable probe with 180° articulation (9535-A/9545-A) for accessing confined or offset ducts
• Onboard data logging capacity of 12,700 timestamped samples and up to 100 named test groups, with automatic start/stop triggers and interval-based recording
• Integrated USB interface and bundled LogDat2™ software for traceable data export, statistical analysis (min/max/avg/std dev), and report generation compliant with GLP and internal QA protocols

Sample Compatibility & Compliance

The VelociCalc® series is validated for use in non-corrosive, non-explosive, particle-laden airstreams typical of commercial, industrial, and cleanroom ventilation systems. Probe sensors meet IEC 61000-4 electromagnetic compatibility standards and are rated for continuous operation within –18°C to +93°C ambient environments and 0–95% RH (non-condensing). While not intrinsically safe, the instruments are routinely deployed in accordance with ASHRAE Guideline 12–2020 (Infection Control Risk Assessment), ISO 16813:2016 (IAQ performance criteria), and FDA-recommended HVAC monitoring practices for pharmaceutical manufacturing. Calibration certificates (NIST-traceable) are provided with each unit, documenting as-found/as-left data per ISO/IEC 17025 requirements. The devices support audit-ready documentation workflows, including operator ID tagging, location metadata, and timestamped calibration history within LogDat2™.

Software & Data Management

LogDat2™ is a Windows-based application enabling secure, version-controlled data handling. It supports 21 CFR Part 11-compliant features including electronic signatures, audit trails, and role-based access control when configured with enterprise IT policies. Users can generate customizable PDF reports containing raw datasets, statistical summaries, trend plots, and annotated duct cross-section diagrams. Export formats include CSV, Excel (.xlsx), and XML for integration into LIMS or CMMS platforms. All logged data retain embedded environmental context (e.g., ambient RH drift compensation applied during post-processing), ensuring metrological traceability from field measurement to final report.

Applications

• HVAC system commissioning and TAB (Testing, Adjusting, Balancing) per NEBB Procedural Standards
• Fume hood face velocity mapping and alarm threshold verification (ANSI/AIHA Z9.5)
• ISO Class 5–8 cleanroom supply air uniformity and velocity profiling
• Duct traverse measurements per ASHRAE Standard 111 (Instrumentation for Air Flow Measurement)
• Room air change rate validation for infection control and pressurization integrity
• Energy audit baseline assessments and retrocommissioning airflow diagnostics

FAQ

What is the difference between the 9535 and 9545 models?
The 9535 measures velocity and temperature only; the 9545 adds integrated RH sensing and calculates dew point and wet-bulb temperature.
Is the ±3% accuracy specification valid across the full 0–30 m/s range?
No — the ±3% accuracy applies only to readings between 0.15 m/s and 30 m/s. Below 0.15 m/s, resolution remains 0.01 m/s but uncertainty increases; refer to TSI Application Note AN-107 for low-velocity uncertainty modeling.
How does temperature compensation affect measurement validity outside 5–65°C?
Velocity readings require manual correction using the stated thermal coefficient (±0.03°C/°C) when ambient temperature deviates from 25°C; this is implemented automatically in LogDat2™ during post-processing if ambient temperature is logged.
Can the VelociCalc® be used in saturated or condensing environments?
No — operation is limited to non-condensing humidity (0–95% RH). Condensation on the hot-wire sensor causes irreversible drift and requires professional recalibration.
Does the instrument support external probe interchangeability?
No — all models use proprietary, factory-calibrated multi-sensor probes; replacement probes must be ordered as matched assemblies (e.g., 9535-A probe assembly P/N 9535A-PROBE) to preserve NIST-traceable calibration.