Humidity calibrator uses PID control

Edited by the Engineeringtalk editorial team Sep 17, 2004

A new portable instrument for calibrating humidity and temperature instrumentation features a Eurotherm PID multiloop controller for accurate set-point adjustment.

A new portable instrument for calibrating humidity and temperature instrumentation, has been launched by Rotronic Instruments.

Designed in the UK, the HygroGen, is a self-contained generator of controlled percentage relative humidity and temperature environments.

It requires no external resources except mains power, and is light enough to be portable for use on-site across a range of industries.

The instrument features a Eurotherm PID multiloop controller for accurate set-point adjustment.

The HygroGen uses a divided flow method for generating the percentage relative humidity required by the user; a desiccant cell provides low humidity and a custom saturator high humidity.

Temperature is controlled using a Peltier element.

Measurement and control are provided by a combination of a Rotronic HygroClip S probe and a Eurotherm 2704 controller.

The controller enables set-points to be accurately adjusted, either via the controller front panel, and/or via a standard RS232 interface and software.

A key advantage of the new instrument is the speed it takes to reach equilibrium of the set values, which means that a multiple point calibration check can be performed in minutes, rather than hours.

A further feature of the calibration chamber is the provision of two additional probe connection points, enabling calibrated reference probes to be added.

Where a primary measurement method is required, such as a condensation hygrometer, an optional rear sampling loop may be specified (HygroGen 2).

This configuration flexibility ensures that the HygroGen can continue to be used whilst the preferred reference instrumentation is itself being calibrated.

Because of its integrated temperature control, the instrument enables calibrations to be performed at a defined and constant temperature, irrespective of the ambient conditions, making the HygroGen especially suitable for on-site calibrations.

It is also possible to calibrate on-site equipment at normal working temperature and humidity conditions.

Measuring just 96 x 96 x 150mm, the Eurotherm 2704 is a high stability temperature and process controller with a high visibility graphical user interface.

This enables it to provide many advanced features such as PV/SP trending.

It is available in a single, dual or triple loop format and is capable of storing up to 50 control programs, each profiling up to three set-points.

This makes it particularly suitable for use in OEM projects like the HygroGen.

The 2704 has both fixed and modular IO and can use a standard expansion unit to provide further input and output connections.

Using internal Toolkit Blocks, customised user configurations and special machine controllers can be created.

Like all Eurotherm controllers, it comes with built-in communications capabilities, including Modbus, Profibus and DeviceNet protocols.