Thermal dispersion flow switches with diagnostics

Flow Measurement & Control

January 2006 Flow Measurement & Control

The new Thermatel TD1 and TD2 from Magnetrol International are the only thermal dispersion flow switches on the market with continuous diagnostics. The TD1/TD2 are designed for harsh process applications in hazardous areas and service flow, level or interface applications. The majority of typical applications handle flow control/flow trending of both gases and liquids.

The Thermatel TD1/TD2 replaces the popular TDF/TSF series, with improved temperature compensation, reduced hysteresis and add on features such as continuous diagnostics, mA output and local LED indication of flow (TD2). The enhancements result in better repeatability, faster response time and easier set up in the field.

The TD1/TD2 diagnostics continuously monitor the signal from the sensor. If this signal goes out of range due to either a failed sensor or failed electronics, the switch will indicate a fault and the relay will de-energise. Both TD1 and TD2 will give a local error indication via a blinking LED, but the TD2 will additionally send a 3,6 or 22 mA error signal to the control room. This feature can be very beneficial in critical service applications that require the user to ensure that the switch is operational.

Thermal dispersion switches are typically affected by sudden process temperature changes. The built-in temperature compensation of the TD1/TD2 reduces this effect to a minimum giving the benefit of a fast response and repeatable switch. Most switches require a substantial change in flow rate for the switch to reset. For instance with a set point of 0,006 m/s for low flow detection, the flow may have to increase between 0,009 and 0,012 for the switch to reset. This causes difficulties in some applications. With the new TD1/TD2 the hysteresis between alarm and reset has been decreased to reduce this potential difficulty. Hysteresis in water will range between 2% and 10% change.

Another feature of the TD2 is the mA output, which can be used for trending and diagnostics. The non-linear mA output cannot be scaled by the user but does provide a repeatable indication of switch operation. While not a transmitter, the mA output of the TD2 can be helpful by providing a repeatable trend indication of the flow rate.

User friendliness is always a key factor in the development of a new Magnetrol product. The TD1/TD2 uses a constant power to the sensor, meaning calibration can be performed faster and easier than competitive units. The units can operate up to 41,3 MPa and can withstand temperatures from -70 up to +450°C. In conclusion, Thermatel Model TD1/TD2 flow/level/interface switches offer a new level of performance and reliability not found in previous switches. The picture shows the Thermatel TD1/TD2 switch for low flow pump protection on cooling installation.

For more information contact NIC, 011 786 3700, www.magnetrol.com

Share this article:

Flow Measurement & Control

Thermal dispersion flow switches with diagnostics

Further reading:

Published by Technews