Michell Instruments SF52 User Manual

SF52 User’s Manual
16 97224 Issue 5, June 2017
APPENDIX C
• Cleanliness of the environment will affect different hygrometers in different
ways. Dust and airborne droplets should be avoided or fi ltered out if possible.
Contaminants can come from the most surprising sources, ordinary urban
pollution, for example.
• The readings given by some types of hygrometer are sensitive to gas type. For
any Instrument which reads in terms of mass per unit volume, e.g. in grams per
cubic metre, it must be confi rmed whether the calibration is valid for the gas in
use.
• Avoid using instruments in direct sunlight or near any other source of heat,
unless they are suitably shielded to prevent measurement errors.
Sampling in general
• Relative humidity measurements should be carried out at a representative
temperature. Failure to allow temperature equilibration will lead to a false
indication of the relative humidity.
• Variations in vapor pressure from place to place can occur where an environment is
subject to any addition or removal of water. If so, care must be taken over where
to make a measurement in order to obtain a representative result.
• Sources and sinks of water vapor should be avoided in any sampling system.
Invasion of stray water can be minimised by attention to leaks, hygroscopic
materials, droplets and condensation. The lower the humidity, the more critical
these precautions are.
• Hygroscopic materials should be avoided. Many materials contain moisture as part
of their structure, particularly organic materials (whether natural or synthetic),
salts (or anything which contains them), and anything which has small pores.
Temperature changes can increase the tendency of these materials to affect the
humidity of the surrounding air.
• Condensation in a sampling process can invalidate humidity measurements by
reducing the water content of the gas being measured. What is more, condensed
liquid may alter the humidity elsewhere by dripping or running to other locations
and evaporating there. In these circumstances, measurement results may be
misleading if hygrometer location is not considered carefully.
• Water droplets or mist must be avoided. These can result in overestimates of the
humidity of the air between the droplets. Such results may exceed 100% RH, or
may be impossible to interpret meaningfully. Droplets of liquid also damage some
electrical types of humidity sensor. Filtering the air sample can eliminate droplets.
• If pumps are used for sampling gas, these should be located after the hygrometer,
to avoid contaminating the measurement environment. Where possible, oil
free pumps should be used, or fi lters employed. Oscillations in pressure due
to pumping can sometimes be reduced or buffered using a needle valve or a
reservoir of large volume.
• Special treatments such as fi ltration can change the amount of moisture in a gas.
Some drying agents take out other gases too.
• When sealing any sensor or probe into a port or manifold in a duct or chamber,
leaks through the probe or electrical cable should be considered. These are not
always sealed against passage of ambient air.
• Where sampling involves a step change in temperature, pressure or gas fl ow
rate, relative to the process being sampled, results may need to be converted
or interpreted. For example ‘pressure dew point’ will differ from the value found
after expanding the gas sample to atmospheric pressure. Care should be taken
to distinguish between ‘gauge’ and absolute values of pressure.

Michell Instruments SF52 Specifications

General

Power Supply	12 to 28 V DC
Operating Temperature	-40 to +60°C
Protection Rating	IP65
Material	Stainless Steel
Output Signal	4-20 mA
Dew Point Range	-100 to +20 °C
Measurement Range	-100 to +20 °C (-148 to +68 °F) dew point 0 to 100 %RH

Summary

Introduction

SF52 Transmitter Features

Details the key features of the SF52 dew-point transmitter, including measurement range and output options.

Installation Procedures

Instrument Unpacking and Checks

Instructions for checking standard components included in the SF52 transmitter packaging.

Electrical Connections and Schematics

Diagrams showing voltage and mA 3-wire connections for the SF52 transmitter.

Transmitter Mounting Guidelines

Guidance on mounting the SF52 transmitter into sampling blocks or directly into pipes/ducts.

Sample Block Mounting

Procedure for installing the SF52 transmitter into an optional G 1/2" BSP sample block.

Direct Pipeline Mounting

Procedure for directly mounting the SF52 transmitter into a pipe or duct.

Operation and Usage

Sampling Best Practices

Recommendations for obtaining representative gas samples and minimizing measurement errors.

Maintenance and Calibration

Routine Calibration and Re-calibration

Information on routine re-calibration services and recommended intervals for the SF52.

Bonded Seal Replacement Procedure

Details on obtaining replacement bonded seals for the SF52 G1/2-BSP.

Technical Specifications (Appendix A)

Performance Metrics

Details on measurement range, accuracy, repeatability, and stability of the SF52.

Electrical and Mechanical Details

Information on output signal, supply voltage, housing, dimensions, and process connections.

Dimensional Drawings

Diagrams showing the physical dimensions of the SF52 transmitter and sample blocks.

Quality, Recycling, and Warranty (Appendix B)

Compliance Directives and Information

Overview of directives Michell Instruments complies with, including ATEX, RoHS2, and WEEE2.

Humidity Measurement Practices (Appendix C)

Relative Humidity Definition

Explains relative humidity and its common abbreviation RH.

General Measurement Recommendations

Practical advice for accurate humidity measurements and instrument care.

Sampling Environment and Material Guidelines

Guidelines for sampling environments, materials, and avoiding contamination.

Measurement Range Specific Advice

Specific advice for dew point and relative humidity measurements across different ranges.

Return and Decontamination (Appendix D)

Decontamination Certificate Process

Form for declaring the decontamination status of equipment before return or service.

EU Declaration of Conformity

Product Compliance Statement

Declaration stating SF52 compliance with EU directives and relevant standards.