Operating Overview; Condumax Ii User Display And Interface; Calibration - Michell Instruments Condumax II User Manual

Condumax II User's Manual
1.2.2

Operating Overview

At the beginning of a measurement cycle, the sample solenoid valve is closed to trap a
gas sample in the hydrocarbon sensor cell for analysis and the controlled cooling of the
optical surface commences. When the scattered light intensity, measured by the optical
measurement system, reaches a user-set trip point, the temperature of the optical
surface is recorded as the hydrocarbon dew point. After this, the sample gas fl ow is
restored and the optical surface is heated to the temperature set-point. The heating of
the optical surface to an elevated temperature ensures that any hydrocarbon residue is
released from the optical surface before the next measurement cycle.
This measurement process is repeated cyclically at intervals determined by the control
system and pre-set by the operator. The minimum cycle time is 10 minutes and under
ideal conditions, when the condensate formed is suffi ciently volatile to evaporate the
residue, the recovery phase will be approximately 8 minutes. However, in applications
where relatively high hydrocarbon dew points occur (within 10°C of saturation at the
sampling system temperature) then longer cycle times may be required in order to
avoid residue build-up on the optical surface.
The measurement of the water dew point is continuous and the gas sample fl ow is
uninterrupted.
The measured hydrocarbon and water dew-point temperature, pressure, date and
time are stored and indexed in the memory, with the most recent reading logged as
number 1. The temperature and pressure readings are available via both the digital
and analog communications. The date and time are only available through digital
communication.
1.2.3

Condumax II User Display and Interface

The Condumax II User Display and Interface Unit is presented via the circular window
of the enclosure. Operation is achieved by a unique system which allows full control
through the glass of the enclosure cover. The cover is fully detachable for greater
access into the enclosure during the installation and initial set-up of the instrument.
During normal operation of the instrument the cover must remain fully secured.
1.2.4

Calibration

The Condumax II is factory-tested and calibrated prior to delivery. Certifi cation is provided
for the hydrocarbon dew-point sensor and the optional water dew-point sensor, if fi tted.
The hydrocarbon dew-point sensor is calibrated at three points across its operating range
using a certifi ed gas mixture of 10% (mol) n-butane in pure nitrogen. The calibration gas
is a gravimetric mixture produced using weights traceable to National Physical Laboratory
(NPL). Calculation of the relationship between calibration gas pressure and hydrocarbon
(n-butane) dew-point temperature is determined using the Peng/Robinson equation of
state. The sensor is also performance tested against samples of synthetic natural gas,
to confi rm the correct optical response to multiple condensable components. These
speciality gas mixtures are analyzed by a UKAS accredited laboratory in accordance with
BS EN ISO 17025.
The water dew-point sensor is supplied with its own Calibration Certifi cate, providing
direct traceability to both UK (NPL) and US (NIST) Humidity Standards. The sensor is
certifi ed at 7 dew-point levels across its operating range against a certifi ed reference
hygrometer, using a mass-fl ow humidity generator system as a source of reference
calibration gas (refer to Section 4.1 for details on calibration maintenance).
Michell Instruments
INTRODUCTION
3