Cole-Parmer Model 32708-00 Economical Thermal Mass Flow Controller

Overview

The Cole-Parmer Model 32708 Series is an economical yet technically robust thermal mass flow controller engineered for precise, repeatable gas flow regulation in laboratory and light-industrial process applications. Utilizing constant-temperature anemometry (CTA) — a well-established thermal sensing principle — the device measures mass flow rate directly by detecting heat transfer between a heated sensor element and the flowing gas stream. This method eliminates dependence on gas density variations caused by pressure or temperature fluctuations, enabling stable operation across defined operating envelopes. The 32708-00 variant serves as the base configuration for 0–50 standard cubic centimeters per minute (sccm) flow control, while the 32708-22 and 32708-32 represent display-equipped and multi-gas-calibrated versions respectively. All units are factory-calibrated for three common process gases: air, helium (He), and argon (Ar), with DIP-switch selection ensuring correct thermal property compensation without software intervention.

Key Features

• Thermal mass flow sensing with ±1.5% full-scale accuracy and ±0.5% full-scale repeatability under specified conditions (gas temperature: 18–25°C; inlet pressure: 5–40 psia)
• 0–5 VDC analog interface supporting both remote setpoint control (input) and real-time flow monitoring (output), facilitating seamless integration into PLC-based or PC-driven control architectures
• 3½-digit LCD display (models 32708-2x and 32708-3x) with mechanical tilt adjustment up to 90° for ergonomic viewing in panel-mounted or benchtop installations
• Gas-selectable via front-panel DIP switches — no firmware updates or external configuration tools required
• Compact form factor (3.125″ W × 3.75″ H × 1″ D, excluding fittings) with standardized mounting footprint suitable for OEM integration or modular process skids
• Wetted materials include 316 stainless steel, anodized aluminum, brass, PTFE, and acetal — selected for chemical compatibility with inert and non-corrosive gases and validated for long-term stability in clean, dry gas streams
• Integrated 3-in-1 power/input/output cable simplifies wiring and reduces point-of-installation connector count, minimizing potential leakage paths and electrical noise susceptibility

Sample Compatibility & Compliance

The 32708 Series is explicitly calibrated and validated for use with air, helium, and argon — gases commonly employed in analytical instrumentation (e.g., GC carrier gas control), semiconductor purge loops, environmental chamber conditioning, and small-scale reactor feed systems. It is not rated for corrosive, combustible, or condensable gases (e.g., Cl₂, NH₃, H₂S, or saturated vapor streams). While not certified to IEC 61508 or SIL standards, its design adheres to fundamental safety principles for low-energy pneumatic control devices. Units meet RoHS Directive 2011/65/EU and are constructed in accordance with UL 61010-1 requirements for electrical equipment used in measurement, control, and laboratory use. For regulated environments, the analog 0–5 V output may be logged using Part 11–compliant data acquisition systems when paired with appropriate audit-trail-enabled software.

Software & Data Management

The 32708 Series operates as a stand-alone analog device and does not require proprietary software or drivers. Its 0–5 V output signal is compatible with standard DAQ systems (e.g., National Instruments, Keysight, or Omega data loggers) and SCADA platforms supporting 0–5 V analog input channels. When integrated into automated workflows, the controller supports basic closed-loop functionality via external PID modules or programmable logic controllers. No embedded memory or firmware update capability is provided; calibration parameters are hard-coded during manufacturing and retained without battery backup. For traceability, each unit ships with a factory calibration sheet listing gas-specific K-factors and test conditions per NIST-traceable procedures.

Applications

• Carrier gas flow regulation in benchtop gas chromatography (GC) systems
• Purge flow control for optical enclosures, laser cavities, and FTIR sample compartments
• Feed gas metering in small-scale catalytic reactors and fuel cell test stations
• Leak testing auxiliary flow control where stable, low-flow gas delivery is required
• Environmental simulation chambers requiring inert gas blanket flow management
• OEM integration into analytical instruments where space, cost, and reliability are prioritized over digital communication protocols

FAQ

Is the 32708-32 calibrated for gases other than air, helium, and argon?
No. Calibration is strictly limited to air, He, and Ar. Using the controller with other gases will result in unquantified measurement error due to differences in thermal conductivity and specific heat.

Can the device operate outside the 18–25°C gas temperature range?
Yes, but accuracy degrades at ±0.15% FS per °C deviation from the nominal range. Users must apply correction factors or maintain upstream temperature stabilization for critical applications.

What is the maximum allowable differential pressure across the controller?
The pressure drop at full-scale flow is ≤15 psi. The absolute maximum system pressure rating is 150 psi; exceeding this may compromise seal integrity or sensor performance.

Does the controller support digital communication protocols such as RS-485 or Modbus?
No. It is an analog-only device. Digital interface capability requires external signal conversion hardware.

Are replacement calibration certificates available after initial purchase?
Yes. Cole-Parmer provides recalibration services with NIST-traceable documentation upon request; recalibration intervals should follow internal quality procedures or industry best practices (e.g., semi-annual verification for GMP-aligned operations).