One for all

The author: Dr. Klaus-Peter Mang Head of Product Management Process Analytics, Mettler Toledo

The M400 is a transmitter for process analytical applications which measures the most important electrochemical parameters like pH, ORP, specific conductivity, dissolved oxygen (DO) and oxygen in gas phases (GPO). The measuring functions for all these parameters are available as standard and do not need to be activated by selecting complicated software options or assembling special measuring modules. The device is compatible both with conventional analogue sensors and with state-of-the-art digital sensors. A single transmitter is sufficient to cover the majority of parameters that have to be measured in process analytics. Training, stockkeeping, installation and commissioning are therefore restricted to a minimum. The operator can choose between versions for hazardous and non-hazardous areas. A version with dedicated firmware is available for measuring oxygen in the gas phase. All instruments are designed with two analogue 4…20 mA outputs for processing measured values. The device is energised by the first loop powered output. There are also two digital inputs and outputs (relay contacts) as well as one analogue input for pressure compensation of oxygen measurements in the gas phase. The Hart interface provides four variables for processing measured values or diagnostic information. One device is generally sufficient for all applications and operating conditions, depending on the actual requirements in the field.

The M400 is housed in an aluminium die-cast case. It is controlled on a backlit dot matrix display with plain text menus in eight different languages. The intuitive MMI (man-machine interface) allows all necessary settings to be configured quickly and easily. The instrument has II 2(1)G Ex ib [ia Ga] IIC T4 Gb Atex approval.

The ISM concept involves digital sensors which format the final measured value internally and transmit a digital signal to the device. In contrast to analogue signals, digital signals enable information to be transferred over long distances without any environmental effects like humidity or electromagnetic fields. As well as delivering measured values they also provide further important information. Data transfer between the sensor and transmitter is bi-directional.

Based on the plug-and-measure principle, digital sensors can be pre-calibrated under controlled conditions in the safe area, then simply exchanged at the measuring point. This reduces the length of time in difficult-to-access locations or hazardous areas and minimises complex handling in the field (e. g. for calibration).

Advanced algorithms in the sensor monitor the process conditions and sensor status continuously in real time. Clear recommendations for action are generated and displayed to maintenance personnel.

Thanks to the iSense Asset Management Suite, the sensors can be managed, evaluated and calibrated directly and conveniently on a PC or notebook. To facilitate quality assurance, all sensor data is logged and traceably documented from the initial registration through all calibrations to deactivation.

The two standard analogue 4…20 mA outputs deliver measured values and/or sensor diagnostic data to analogue inputs for further processing. The Hart interface additionally permits bi-directional communication with the transmitter for remote configuration or for processing error messages and sensor diagnostic data, with numerous functions such as four process variables (measured values or sensor diagnostics) or a configuration menu for measurement, analogue outputs, ISM settings and hold output. The M400 supports different calibration procedures (one-point, two-point, process) including calibration history, various warning and error messages and date and time settings. A choice of identification data is also available (e. g. hardware and software version, serial number, etc.).

Device descriptions (DD) can be supplied for most relevant asset management tools like AMS (Emerson) or PDM (Siemens). Tools based on the open FDT standard are likewise possible if a DTM is installed. Maximum compatibility of the M400 instrument is guaranteed for seamless integration in process control systems. With its comprehensive transmitter portfolio Mettler Toledo supports fieldbus application architectures based on Profibus PA and Foundation Fieldbus.

The M400 is optimised for operation in hazardous areas. The two-wire concept with loop powered, intrinsically safe analogue outputs and digital ISM sensors featuring low-power technology means the transmitter is suitable for Zone 1 and the sensors for Zone 0.

Owing to the comprehensive diagnostic functions, the operator is kept permanently in- formed about measuring reliability – essential for efficient maintenance on demand. The cost of ownership is minimised and process safety increased.

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