Michell Instruments SF72 User manual

SF72
Dew-Point Transmitter
User’s Manual
97325 Issue 3
May 2018
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Please fill out the form(s) below for each instrument that has been purchased.
Use this information when contacting Michell Instruments for service purposes.
Transmitter
Code
Serial Number
Invoice Date
Location of Instrument
Tag No
Transmitter
Code
Serial Number
Invoice Date
Location of Instrument
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Transmitter
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© 2018 Michell Instruments
This document is the property of Michell Instruments Ltd. and may not be copied or
otherwise reproduced, communicated in any way to third parties, nor stored in any Data
Processing System without the express written authorization of Michell Instruments Ltd.
For Michell Instruments' contact information please go to
www.michell.com
SF72 Transmitter

SF72 Transmitter User’s Manual
iv 97325 Issue 4, May 2018
Contents
Safety ................................................................................................................................vi
Electrical Safety ...........................................................................................................vi
UL Approval.................................................................................................................vi
Pressure Safety............................................................................................................vi
Toxic Materials .............................................................................................................vi
Repair and Maintenance ...............................................................................................vi
Calibration...................................................................................................................vi
Safety Conformity ........................................................................................................vi
Abbreviations..................................................................................................................... vii
Warnings ...........................................................................................................................vii
1 INTRODUCTION ................................................................................................1
1.1 Features ............................................................................................................ 1
2 INSTALLATION ..................................................................................................2
2.1 Unpacking the Instrument................................................................................... 2
2.2 Preparation of the Sensor Cable .......................................................................... 3
2.3 Cable Connection ............................................................................................... 4
2.4 Electrical Schematic............................................................................................ 4
2.4.1 Electrical Boundaries ..................................................................................... 5
2.5 Transmitter Mounting.......................................................................................... 5
2.5.1 Transmitter Mounting - Sample Block (Optional)............................................. 6
2.5.2 Transmitter Mounting - Direct Pipeline Connection ........................................... 7
3 OPERATION ......................................................................................................8
4 MAINTENANCE ..................................................................................................9
4.1 O-Ring Replacement......................................................................................... 10
Figures
Figure 1 Transmitter Unpacking Method ....................................................................2
Figure 2 Connector Terminal Block Removal ..............................................................3
Figure 3 Wiring Connections.....................................................................................3
Figure 4 Connector Installation.................................................................................4
Figure 5 2-Wire Connection Diagram.........................................................................4
Figure 6 Maximum Load of SF72 - Including Cable Resistance ....................................5
Figure 7 Transmitter Mounting - Sensor Block............................................................6
Figure 8 Transmitter Mounting - Pipe or Duct.............................................................7
Figure 9 Installation Location ...................................................................................8
Figure 10 Indication of Dead Space ............................................................................8
Figure 11 Replacement of HDPE Guard .......................................................................9
Figure 12 Dimensions - SF72 2-Wire .........................................................................13

SF72 Transmitter User’s Manual
Michell Instruments v
Appendices
Appendix A Technical Specifications .............................................................................12
A.1 Dimensions .................................................................................13
Appendix B Quality, Recycling & Warranty Information...................................................15
Appendix C Return Document & Decontamination Declaration........................................17

SF72 Transmitter User’s Manual
vi 97325 Issue 4, May 2018
Safety
The manufacturer has designed this equipment to be safe when operated using the procedures
detailed in this manual. The user must not use this equipment for any other purpose than that
stated. Do not apply values greater than the maximum value stated.
This manual contains operating and safety instructions, which must be followed to ensure the safe
operation and to maintain the equipment in a safe condition. The safety instructions are either
warnings or cautions issued to protect the user and the equipment from injury or damage. Use
competent personnel using good engineering practice for all procedures in this manual.
Electrical Safety
The instrument is designed to be completely safe when used with options and accessories supplied
by the manufacturer for use with the instrument.
UL Approval
This product is UL approved within the operating temperature range of -20°C to +60°C. The IP66
rating of this product is outside the scope of UL Approval, but this product has been verified as being
IP66 by independent, UKAS accredited, 3rd party listing.
Pressure Safety
DO NOT permit pressures greater than the safe working pressure to be applied to the instrument.
The specified safe working pressure is 45 MPa (450 barg / 6500 psig). Refer to the Technical
Specifications in Appendix A.
Toxic Materials
The use of hazardous materials in the construction of this instrument has been minimized. During
normal operation it is not possible for the user to come into contact with any hazardous substance
which might be employed in the construction of the instrument. Care should, however, be exercised
during maintenance and the disposal of certain parts.
Repair and Maintenance
The instrument must be maintained either by the manufacturer or an accredited service agent. For
Michell Instruments’ contact information please go to www.michell.com.
Calibration
The recommended calibration interval for this instrument is 12 months unless it is to be used in a
mission-critical application or in a dirty or contaminated environment in which case the calibration
interval should be reduced accordingly. The instrument should be returned to the manufacturer,
Michell Instruments Ltd., or one of their accredited service agents for re-calibration.
Safety Conformity
This product meets the essential protection requirements of the relevant EU and US standards
and directives. Further details of applied standards may be found in the Technical Specifications in
Appendix A.

SF72 Transmitter User’s Manual
Michell Instruments vii
Abbreviations
The following abbreviations are used in this manual:
barg pressure unit (=100 kP or 0.987 atm) (bar gauge)
ºC degrees Celsius
ºF degrees Fahrenheit
DC direct current
g grams
in inch(es)
m micrometer
m/sec meters per second
mA milliampere
max maximum
mm millimetres
MPa megapascal
Nl/min normal liters per minute
Nm Newton meter
oz ounces
psig pounds per square inch
RH relative humidity
scfh standard cubic feet per hour
fps feet per second
T temperature
V Volts
Ohms
ø diameter
Warnings
The following general warning listed below is applicable to this instrument. It is repeated
in the text in the appropriate locations.
Where this hazard warning symbol appears in the following
sections it is used to indicate areas where potentially hazardous
operations need to be carried out.

SF72 Transmitter User’s Manual
viii 97325 Issue 4, May 2018

SF72 Transmitter User’s Manual
Michell Instruments 1
INTRODUCTION
1 INTRODUCTION
The SF72 dew-point transmitter has been manufactured, tested and calibrated to the
highest available standards and should be in perfect working order, ready for installation
into a gas measurement application. If there are any questions about the instrument
or how to install and operate it, please contact a Michell representative (for Michell
Instruments’ contact information go to www.michell.com).
1.1 Features
The SF72 dew-point transmitter is a continuous on line 4-20mA transmitter for the
measurement of moisture content in air and other non-corrosive gases.
The key features are:
• Compatible with Compressed Air Quality ISO8573.1 class 2 to 6
requirements
• Dew-point measurement range -60 to +60ºCdp (-76 to +140ºFdp)
• Fast response
• Rugged all stainless steel IP66 construction
• 8-point traceable calibration certificate
• Accuracy ±2ºC dew point
• Available in G½” BSP, ¾” - 16 UNF and ” - 18 UNF process connections

SF72 Transmitter User’s Manual
297325 Issue 4, May 2018
INSTALLATION
2 INSTALLATION
2.1 Unpacking the Instrument
On delivery, please check that all the following standard components are in the packing
box:
• SF72 Transmitter
• Bonded Seal
• Certificate of Calibration
• Connector (for sensor/cable)
Unpack the dew-point transmitter box as follows:
G½“ BSP (black)
¾“ UNF (green)
ƙ“ UNF (blue)
87653 421
Figure 1
Transmitter Unpacking Method
1. Unscrew the cap (1) from the packing tube (8).
2. Remove the foam block (3) containing the connector (2).
3. Pull out the transmitter (5) from the tube, complete with the two
foam covers (6) and (7) and the red protective cap (4).
4. Remove the foam covers from the transmitter but leave the plastic
protective cover (5) and the red cap (4) in place until ready for
installation.
NOTE: The transmitter sensing element is protected while in transit by a blue,
green or black cover containing a small desiccant capsule. The connection
pins are protected by a red plastic cap. None of these plastic items are required
for the operation of the transmitter.
NOTE: Keep the connector in a safe place until the transmitter is ready for
wiring.

SF72 Transmitter User’s Manual
Michell Instruments 3
INSTALLATION
2.2 Preparation of the Sensor Cable
The sensor cable is NOT supplied as standard. A cable can be obtained by contacting
your local distributor or Michell Instruments (see www.michell.com for details).
Cable connection to the SF72 transmitter is made via the removable connector. Removing
the central screw enables the connector terminal block to be removed from the outer
housing by using a small screwdriver to prise it clear.
i
O-ring
and washer
Figure 2 Connector Terminal Block Removal
Caution: When removing the central screw ensure that the
small sealing O-ring and the washer are retained on the screw
and are present during re-installation.
For the transmitter to work properly, and to achieve maximum performance, the sensor
cable must be connected to the sensor connector as shown in the drawing below.
NOTE: The drawing below shows the identity of the connector terminals and
wiring connections of the cable manufactured by Michell Instruments.
SCALE 2:1
i
j
SHORT
AS POSSIBLE
h
1
3
24
BLUE
BRAID BRAID
GREEN - 4-20 mA
(SOURCE)
SCREEN
RED
+POWER
GND
VIEW ON REAR
OF CONNECTOR
GREEN
SIGNAL (SOURCE) GREEN
YELLOW
BLUE
RED
h
h
BLUE - SCREEN
RED + POWER
GREEN - 4-20 mA
BLUE - SCREEN
RED + POWER
GN
RD
BL
Figure 3 Wiring Connections
Always connect the 4-20 mA return signal to a suitable load
(see
Figure 3) before the power is applied. Without this
connection, the transmitter may be damaged if allowed to
operate for prolonged periods.

SF72 Transmitter User’s Manual
497325 Issue 4, May 2018
INSTALLATION
2.3 Cable Connection
When installing the connector, and to ensure that full ingress protection is achieved, the
securing screw (with the O-ring and washer) must be tightened to a minimum torque
setting of 3.4 Nm (2.5 ft-lbs). The sensor cable used must be a minimum diameter of
4.6mm (0.2”).
In applications where the ambient temperature is +60°C,
ensure that any connection cable used is also suitably rated.
O-ring
and washer
i
Figure 4 Connector Installation
2.4 Electrical Schematic
NOTE: The screen/shield should be connected for maximum performance
and to avoid interference.
3
1
Max Load
250R @ 12V
500R @ 24V
Supply
12V Min
28V Max
+
Screen/
Shield
Figure 5
2-Wire Connection Diagram

SF72 Transmitter User’s Manual
Michell Instruments 5
INSTALLATION
2.4.1 Electrical Boundaries
100
200
300
400
500
600
12 14 16 18 20 22 24 26 28
Resistance (ohms)
Supply Voltage
Figure 6 Maximum Load of SF72 - Including Cable Resistance
2.5 Transmitter Mounting
Prior to installation of the transmitter, unscrew and remove the black, green or blue
plastic cover and retain for future use. Take care to prevent any contamination of
the sensor before installation (handle the transmitter by the main body only,
avoiding contact with the sensor guard).
The SF72 can be mounted either into a flow-through sensor sampling block (optional) or
directly into a pipe or duct. It can be operated at pressures of up to 45 MPa (450 barg
/ 6500 psig) when fitted with the bonded seal or O-ring provided.
The recommended gas flow rate, when mounted in the optional sampling block, is 1 to
5 Nl/min (2.1 to 10.6 scfh). However, for direct insertion applications, gas flow can be
from static to 10 m/sec (32.8 fps).
NOTE: Pass the seal over the mounting thread and assemble into the sampling
location, by hand, using the wrench flats only. DO NOT grip and twist the
sensor cover when installing the sensor.
When installed, fully tighten using a wrench until the seal is fully compressed and to the
following torque settings:
• G 1/2” BSP 56 Nm (41.3 ft-lbs)
• 3/4” - 16 UNF 40 Nm (29.5 ft-lbs)
• 5/8” - 18 UNF 30.5 Nm (22.5 ft-lbs)

SF72 Transmitter User’s Manual
697325 Issue 4, May 2018
INSTALLATION
2.5.1 Transmitter Mounting - Sample Block (Optional)
(Applicable to the SF72 ⅝” -18 UNF and G½ BSP versions ONLY)
The following procedure must be carried out by a qualified
installation engineer.
To mount the transmitter into the sensor block (preferred method), proceed as follows,
refer to Figure 7.
1. Remove the protective cover (2) and the desiccant capsule (2a) from the
tip of the transmitter (1).
2. Fit the seal (4) over the threaded part of the transmitter body.
WARNING: Under no circumstances should the sensor
guard be handled with the fingers.
3. Screw the transmitter (1) into the sample block (3) and tighten to the
recommended torque setting (see Section 2.2). NOTE: Use the flats of
the hexagonal nut and not the sensor body.
4. Fit the transmitter cable/connector assembly to the plug located on the
base of the transmitter and tighten the fixing screw (see Section 2.2).
3
4
1
2
2a
Figure 7 Transmitter Mounting - Sensor Block

SF72 Transmitter User’s Manual
Michell Instruments 7
INSTALLATION
2.5.2 Transmitter Mounting - Direct Pipeline Connection
The transmitter may be directly mounted into a pipe or duct as shown in Figure 8.
CAUTION: Do not mount the transmitter too close to the
bottom of a bend where any condensate in the pipeline
might collect and saturate the probe.
The pipe or duct will require a thread to match the transmitter body thread. Fixing
dimensions are shown in Figure 8. For circular pipework, to ensure the integrity of a
gas tight seal, a mounting flange will be required on the pipework in order to provide a
flat surface to seal against.
The following procedure must be carried out by
competent personnel.
1. Ensure that the protective cover and the desiccant capsule have been
removed from the tip of the transmitter (3).
WARNING: Under no circumstances should the
sensor guard be handled with the fingers.
2. Fit a seal (2) over the threaded part of the transmitter body.
3. Screw the transmitter (3) into the pipe. Tighten enough to obtain a gas
tight seal. (Torque will depend upon the pipeline material.) NOTE: Do
not overtighten or the thread on the pipework may be stripped.
14 15 16 17 18 18 20 21 22 23
2345678910 11
1
2
3
48mm
1
2
3
Figure 8 Transmitter Mounting - Pipe or Duct

SF72 Transmitter User’s Manual
897325 Issue 4, May 2018
OPERATION
3 OPERATION
Operation is very simple assuming the following installation techniques are adhered to:
Sampling Hints
Be Sure the Sample is Representative of the Gas Under Test:
The sample point should be as close to the critical measurement point as possible. Also,
never sample from the bottom of a pipe as entrained liquids may be drawn into the
sensing element.


Figure 9
Installation Location
Minimize Dead Space in Sample Lines:
Dead space causes moisture entrapment points, increased system response times and
measurement errors, as a result of the trapped moisture being released into the passing
sample gas and causing an increase in partial vapor pressure.
Deadspace

Figure 10 Indication of Dead Space
Remove Any Particulate Matter or Oil from the Gas Sample:
Particulate matter at high velocity can damage the sensing element and similarly, at
low velocity, they may ‘blind’ the sensing element and reduce its response speed. If
particulate, such as degraded desiccant, pipe scale or rust is present in the sample gas,
use an in-line filter, as a minimum level of protection. For more demanding applications
Michell Instruments offers a range of sampling systems (for more information contact
www.michell.com).
Use High Quality Sample Tube and Fittings:
Michell Instruments recommends that, wherever possible, stainless steel tubing and
fittings should be used. This is particularly important at low dew points since other
materials have hygroscopic characteristics and adsorb moisture on the tube walls,
slowing down response and, in extreme circumstances, giving false readings. For
temporary applications, or where stainless steel tubing is not practical, use high quality
thick walled PTFE tubing.
Position Transmitter away from Heat Source:
It is recommended, as good instrumentation practice, that the transmitter is placed
away from any heat source to avoid adsorption/desorption.

SF72 Transmitter User’s Manual
Michell Instruments 9
MAINTENANCE
4 MAINTENANCE
Calibration
Routine maintenance of the SF72 is confined to regular re-calibration by exposure of
the SF72 to sample gases of known moisture content to ensure that the stated accuracy
of the SF72 is maintained. Calibration services traceable to the UK
National Physical
Laboratory
(NPL) and the US National Institute of Standards and Technology (NIST) are
provided by Michell Instruments.
Michell Instruments offers a re-calibration service to suit specific needs. A Michell
representative can provide detailed, custom advice (for Michell Instruments’ contact
information go to www.michell.com).
Sensor Guard Replacement
The sensor is supplied with a white HDPE guard (standard) or a stainless steel guard
(if specified at time or order). The method of replacement is the same for both types.
HDPE Guard
The HDPE guard provides <10m protection to the dew-point sensor. It is designed
to show any contamination and the guard should be changed if the surface becomes
discolored.
When replacing the guard, care should be taken to handle the guard by the bottom part
only. Replacement guards (EA2-HDPE) - pack of 10 - can be obtained by contacting
Michell Instruments (www.michell.com) or your local distributor.
x
HANDLE,
USING
GLOVES, BY
BLACK PART
ONLY
S
/
N
o
.
F
A
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0
-
2
9
3
P
r
o
d
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o
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e
:
S
F
7
2
-
T
-
6
0
/
+
6
0
S
F
7
2
T
r
a
n
s
m
i
S
c
a
l
e
d
R
a
n

-
-
Figure 11 Replacement of HDPE Guard
Stainless Steel Guard
The stainless steel guard provides <80m protection to the dew-point sensor. It is
designed to show any contamination and the guard should be changed if the surface
becomes discolored.
When replacing the guard, care should be taken to handle the guard by the bottom part
only. A replacement guard (SSG) can be obtained by contacting Michell Instruments
(www.michell.com) or your local distributor.
Bonded Seal
If the installed bonded seal gets damaged or lost, a pack of 5 replacement bonded seals
can be obtained by contacting Michell Instruments, or your local distributor, and quoting
part number 5/8-BS.

SF72 Transmitter User’s Manual
10 97325 Issue 4, May 2018
MAINTENANCE
4.1 O-Ring Replacement
Do not touch the filter with bare hands
1. Identify the O-ring to be removed, as shown below.
BS116 (3/4” x 3/32”) viton,
75 shore
2. Carefully slide tweezers, thin bladed screwdriver or a blunt needle under
the outer edge of the O-ring. NOTE: Take care not to scratch any of
the surfaces of the surrounding metal component.
3. Move the tool around the circumference to assist the extraction process.
Slide the O-ring clear of the thread and filter.
4. Make sure the groove has no scratches and is free from grease, dirt
or debris. Slide the new O-ring over the filter and thread and into the
groove. NOTE: Do not touch the filter with bare hands.

SF72 Transmitter User’s Manual
Michell Instruments 11
APPENDIX A
Appendix A
Technical Specifications

SF72 Transmitter User’s Manual
12 97325 Issue 4, May 2018
APPENDIX A
Appendix A Technical Specifications
Performance
Measurement Range (Dew
Point) -60 to +60ºCdp (-76 to +140ºFdp)
Accuracy (Dew Point) ±2ºCdp (±3.6ºFdp)
Repeatability ±0.2ºCdp (±0.36ºCdp)
Long Term Stability <1% per annum
Calibration Traceable 8-point calibration certificate
Electrical Specifications
Output Signal 4-20mA (2-wire) current source
Output Dew point
Analog Output Scaled Range
Standard -60 to +60°C (-76 to +140ºF)
-50 to +50°C (-58 to +122ºF)
-50 to +30°C (-58 to +86ºF)
Non-standard available upon request
Supply Voltage 12 to 28 V DC
Load Resistance Max 250 @ 12 V (500 @ 24 V)
CE conformity Approved
UL61010-1 & CAN/CSA C22.2 No. 61010-1
Operating Specifications
Operating Temperature -40 to +60ºC (-40 to +140ºF)
Operating Pressure 45 MPa (450 barg / 6500 psig) max
Overpressure Rating x 2 operating pressure 90 MPa (900 barg / 13,000 psig)
Flow Rate
1 to 5 Nl/min (2.1 to 10.6 scfh) mounted in standard sampling
block;
0 to 10 m/sec (0 to 32.8 fps) direct insertion
Thermal Compensation Characterized over operating range
Mechanical Specifications
Ingress Protection IP66 in accordance with standard BS EN60529:1992
NEMA 4 in protection accordance with standard NEMA 250-2003
Housing Material 316 stainless steel
Dimensions Transmitter plus connector
L=132mm x ø45mm (5.19” x ø1.77”)
Sensor Guard Standard: HDPE Guard < 10m
Optional: 316 stainless steel sintered guard < 80m
Process Connection
G½” BSP
¾” - 16 UNF
” - 18 UNF
Weight 150g (5.29oz)
Interchangeability Fully interchangeable transmitter
Electrical Connections Hirshmann GDS Series (DIN 43650-C)
Digital Diagnostic
Communications RS485, 2-wire Modbus RTU