Michell S8000 Precision Chilled Mirror Hygrometer

Overview

The Michell S8000 is a precision chilled mirror hygrometer that provides a direct measurement of dew point, temperature and pressure with ±0.1 °C dew point accuracy across a range of -60 to +40 °C dew point. Because it measures the fundamental temperature at which condensation forms rather than inferring humidity from a material property, the instrument delivers long-term, drift-free results and is widely used as a reference for calibrating other humidity and dew point sensors. From the measured dew point it calculates ppmV, ppmW, absolute humidity and relative humidity.

Seven Star LLC supplies the Michell S8000 to calibration laboratories, power utilities, compressed air users and research facilities in Oman and the GCC, with engineering support in Muscat. We help customers choose between the low pressure and high pressure versions, the optional internal pressure transducer, the remote PRT temperature probe and accredited calibration options, so the hygrometer fits the role it will play in their quality system.

Measurement Principle

In the Michell S8000, an LED focuses a beam of light of fixed intensity onto a temperature-controlled mirror. As a thermoelectric cooler chills the mirror, condensate forms and scatters the light. The RRS triple detection optics use one photodetector to measure reflected light, a second to measure scattered light and a third reference detector to monitor the LED itself and compensate for temperature effects. These signals drive the cooler to hold the mirror in equilibrium, where evaporation and condensation occur at the same rate; at that point the mirror temperature, measured by a platinum resistance thermometer, equals the dew point of the gas.

Below 0 °C, super-cooled water can remain on a mirror and give errors of up to 10% of reading if it is mistaken for ice. The FAST frost assurance technology detects when the mirror is in that region and rapidly cools it until a defined ice film forms, guaranteeing that all readings below 0 °C are frost points. An optional viewing microscope lets the operator inspect the mirror directly. DCC dynamic contamination correction periodically rebalances the optics to compensate for any loss of light caused by contamination, keeping performance stable without manual mirror cleaning cycles.

Engineering Design of the Michell S8000

The Michell S8000 is a benchtop instrument measuring 187 x 440 x 343 mm and weighing 12.3 kg, powered from 85 to 264 V AC. It is offered in a low pressure version for 0 to 1 barg and a high pressure version for 0 to 20 barg, with 6 mm Swagelok male process connections and a recommended sample flow of 750 ml/min within a 500 to 1000 ml/min range. An integrated flow sensor reports sample flow, and an optional internal pressure sensor with 0 to 25 bara or 0 to 1.6 bara range provides real-time pressure for stable calculation of pressure-dependent values.

On the front panel of the Michell S8000, a 5.7 inch touchscreen LCD shows customizable readings, trend graphs and fault warnings. Two analog outputs are user selectable as 4 to 20 mA, 0 to 20 mA or 0 to 1 V, and two volt-free changeover contacts give one process alarm and one fault alarm. Digital communication uses Modbus RTU over USB or Modbus TCP over Ethernet, and data is logged to an SD card of up to 32 GB, enough for about 24 million logs or 560 days at 2 second intervals. Application software allows full control of the instrument from a PC.

Key Features

The main reasons laboratories and plants choose the Michell S8000 are listed below.

• Dew point accuracy of ±0.1 °C with ±0.05 °C reproducibility, based on a fundamental, low-drift measurement.
• Measurement range of -60 to +40 °C dew point, with a remote Pt100 probe option for air temperature measurement.
• RRS triple optics give high sensitivity and fast response even at low frost points where condensate forms slowly.
• FAST frost assurance guarantees that measurements below 0 °C are made over ice, not super-cooled water.
• DCC dynamic contamination correction automatically compensates for optical contamination.
• Operation at up to 20 barg with the high pressure version, and an optional internal pressure transducer.
• Two configurable analog outputs, two alarm relays, Modbus RTU over USB and Modbus TCP over Ethernet.
• Three-point traceable calibration as standard, with UKAS accredited calibration available as an option.

Industrial Applications

The manufacturer lists the Michell S8000 for standards laboratory reference work, transformer vacuum drying verification, clean and dry room monitoring, metallurgical process monitoring, commercial calibration laboratory reference, compressed air dryer development and hydrogen fuel cell research. In each case the value of the Michell S8000 is the same: a measurement that can be trusted without assuming that a sensor has kept its calibration, which makes it the yardstick against which field transmitters are checked.

In Oman, typical users include instrument calibration workshops at oil and gas operators and service companies, transmission utilities verifying the drying of power transformers before energization, and facilities in Muscat, Sohar and Salalah that run controlled dry rooms or high-specification compressed air. Seven Star LLC supplies the Michell S8000 together with the field instruments it is used to verify, such as the Michell Easidew EA2 dew point transmitter, the Easidew PRO I.S. moisture transmitter and the Vaisala DMT152 dew point transmitter.

Technical Specifications

The following Michell S8000 values are taken from the manufacturer datasheet; options such as the pressure sensor and remote probe should be confirmed at order.

How to Order

To request a quotation for the Michell S8000, tell Seven Star LLC the dew point range and pressure you need to measure, whether the instrument will serve as a laboratory reference or a process monitor, and which options and calibration certificate you require. Download the datasheet from this page for technical review, and contact our Muscat instrumentation team for availability, delivery times and support across Oman and the GCC.