E&H DTT thermal flow switch

E&H DTT thermal flow switch

1. Product Series Overview: DTT31 vs. DTT35

The Endress+Hauser Flowphant T series comprises two primary thermal dispersion flow switch variants designed for distinct industrial environments: the DTT31 for general industrial applications and the DTT35 for hygienic/ sanitary processes.

DTT31 features threaded connections (NPT or G male threads) with stainless steel construction, making it suitable for monitoring cooling water circulation, pump lubrication systems, leak detection in process lines, and filter monitoring across a broad range of industrial settings.-4

DTT35 is specifically engineered for hygienic applications, incorporating 3-A sanitary standards and EHEDG certification, with process connections including Tri-Clamp, Varivent, DIN 11851, and APV-Inline.-8-9

Both models deliver practically no pressure loss and operate on the same thermal dispersion principle, measuring relative mass flow rates from 0.03 to 3 m/s (0.1 to 9.84 ft/s).-4

2. Technical Specifications at a Glance

Source:-2-9

3. Featured Model Deep Dive: DTT31-A1A111AAX1AA

The DTT31-A1A111AAX1AA represents a standard configuration within the Flowphant T DTT31 series, configured for general industrial flow monitoring applications with threaded process connection and basic electrical output configuration.

Below is the order code breakdown for this specific model:

This model is designed for safe measurement, display, and monitoring of relative mass flow rates of liquid media across industrial process lines, with practically no pressure loss.-43

Other configurable variants in the DTT31 family include:

DTT31-A1B111AE2AAB – With 4-20mA analog output for flow percentage-43

DTT31-A1A111AB2AAB – Alternative output configuration-

DTT31-A1C111DE2AAB – 30mm probe length-2

DTT31-A1C111DE2BAB – 50mm probe length-2

DTT31-A1A111DAX1AB – 45mm probe length-2

DTT31-A1C111DEX1AB – 152mm probe length-2

The DTT35 family includes configurations such as DTT35-A3A111DL2BAB (Tri-Clamp connection, 2″ size)-8, DTT35-A1C111DL2AAA (Clamp ISO2852 DN40-51)-44, and DTT35-A1B111PH2AAA.

4. Thermal Dispersion Measuring Principle

The Flowphant T series operates on the calorimetric (thermal dispersion) measuring principle. This method uses a heated temperature sensor that is continuously heated above the process medium temperature. As liquid flows past the sensor, forced convection dissipates heat from the sensor element. The cooling effect is directly proportional to the mass flow velocity.-

Key technical characteristics of this measuring principle:

Measures relative mass flow as a percentage between 0% and 100%-4

The device internally compares the heated sensor temperature against a reference sensor

Switch point can be configured across the entire 0.03 to 3 m/s measuring range

The principle is sensitive to disturbed flow conditions; proper installation away from elbows, valves, and pumps is required for optimal accuracy-

5. Applications and Industry Use Cases

The DTT31 and DTT35 flow switches are deployed across a wide range of industrial process monitoring applications:

Cooling water circulation systems

Pumps, turbines, compressors, and heat exchangers-1-4

Leak monitoring

Process lines, cooling circuits, and critical piping networks-1

Pump functionality monitoring

Dry-run protection, flow verification, and pump health assessment-4

Lubrication systems

Lubrication circuit monitoring for rotating machinery-1

Filter monitoring

Beverage industry filtration systems and general industrial filter integrity verification-1-9

6. Order Code Structure & Configuration Variants

Endress+Hauser employs a modular order code system for the Flowphant T series. Each DTT31 or DTT35 model is built by selecting options across multiple feature positions.

The complete order code for any DTT unit comprises:

Available DTT31 process connections include: ANSI NPT ¼″, NPT ½″, and G male threads in various sizes. DTT35 supports hygienic connections including Tri-Clamp ISO2852, Varivent F and N, DIN 11851, and APV-Inline.-4

7. Installation Guidelines

Proper installation is critical for accurate flow monitoring. Key installation requirements for DTT31 and DTT35 models:

Flow conditioning

Install away from flow disturbances such as elbows, reducers, valves, and pumps-

Minimum recommended straight-run lengths upstream and downstream of the sensor

The thermal measuring principle is sensitive to disturbed flow conditions

Orientation flexibility

Top housing section can be rotated 310° after installation-4

Rotatable display enables reading of measured values in all orientations

Environmental considerations

IP66 degree of protection for outdoor or washdown environments

Ambient temperature range must be maintained within specifications

CIP temperatures up to 130°C (266°F) are permissible for cleaning cycles-9

8. Electrical Connections and Output Options

The Flowphant T series supports multiple output configurations to suit different control system requirements:

Output configuration options:

1x PNP switch output – Basic on/off flow monitoring (as in DTT31-A1A111AAX1AA)

2x PNP switch outputs – Dual setpoint monitoring

1x PNP switch + 4-20mA analog output – For flow rate as percentage or temperature-4

Key electrical specifications:

Supply voltage: 18 to 30 V DC-2

Overcurrent protection: Automatic switching current testing every 0.5 seconds; output disconnects under overcurrent-4

Max capacitance load: 14 μF at max supply voltage

Electrical connections:

M12 plug connector (standard for most configurations)

Cable gland options available for certain order code variants-44

Operation and configuration:

Onsite operation via three keys on the device-

Configuration software (FieldCare / ReadWin) for quick configuration and reliable storage of device settings-1

Digital display and LEDs assist navigation through the operating menu

9. Certifications and Approvals

The Flowphant T series carries multiple certifications validating its suitability for various industrial and hygienic applications:

The DTT35 specifically meets the requirements of Sanitary Standard No. 74-03, confirmed by the 3-A symbol on the device nameplate (not applicable for conical metal-to-metal process connections).-24

The CE mark confirms compliance with EU Directives, EN 61010-1 “Protection Measures for Electrical Equipment,” and EMC requirements of IEC/EN 61326.-24

10. Comparison: DTT31 vs. DTT35