Michell Instruments SF52 User Manual

SF52 User’s Manual
18 97224 Issue 5, June 2017
APPENDIX C
• Clean environments are always best for humidity measurements, but this is
especially critical at very low humidity. Even fi ngerprints harbour water. High
purity cleaning agents are recommended: Analytical Reagent (AR) quality solvents
for oil-based contaminants, and purifi ed water (distilled or de-ionised) for salts.
Cleaning should be followed by thorough drying by a clean method.
• Sample tubing should be as short in length as possible. The surface area should
be minimised by using the narrowest tubing that the fl ow conditions will permit.
• Avoid leaks. Minimising the number of connections (elbows, tees, valves, etc.)
helps with this.
• Adequate fl ow of the gas sample should be ensured, to minimise the infl uence of
sources of stray water in the fl ow path.
• ‘Dead ends’ should be avoided, as they cannot easily be fl ushed.
• Back-diffusion of moisture should be minimised, e.g. by fast fl ow rates of gas,
long exhaust tubes after the sensor, or by valves which isolate the low-humidity
region from ambient air.
Practical recommendations for specifi c types of hygrometer
Relative humidity capacitive sensor
• Care should be taken to avoid mechanical shock (impact) or thermal shock
(sudden temperature changes). Sensors should be protected from steam or
water sprays, and from direct sunlight.
• Where a sensor is at risk of exposure to dust, droplets, or the occasional knock
during handling, the appropriate guard or fi lters for the sensor head should be
used.
• Any temptation to breathe on the sensor, or to wave it over cups of tea, etc.
should be resisted. Filters and saturation guarding may protect the sensor, but
these actions carry a risk of damage by condensation or other contamination.
• Protective fi lters can slow the response time of sensors. This can be avoided by
removing any fi lter, but the benefi t must be weighed against the risk of damage
to the sensor.
• Sensors should not normally be submerged in liquids. In the case of a resistive
(electrolytic) sensor, water or other liquids would certainly damage the sensor
beyond repair.
• Salt solutions are especially commonly used for calibration of electrical sensors,
and should be provided with traceability directly or via a calibrated hygrometer.
Protection of sensors from direct contact with salt or solution is most important
as contamination would destroy or seriously impair the sensing element.

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.