Schmidt SS 20.420 User manual

SCHMIDT®Flow Sensor
SS 20.420
Instructions for Use

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 2
SCHMIDT®Flow Sensor
SS 20.420
Table of Contents
1Important Information ......................................................................3
2Application Range ...........................................................................4
3Mounting Instructions ......................................................................5
4Electrical Connection.....................................................................10
5Signalizing .....................................................................................12
6Startup...........................................................................................13
7Information on Operation...............................................................14
8Service Informations......................................................................15
9Technical Data...............................................................................18
10 Declarations of Conformity............................................................19
Impressum:
Copyright 2021 SCHMIDT Technology GmbH
All rights reserved
Revision: 538888.02E
Subject to modifications

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 3
1 Important Information
These instructions for use contain all required information for a fast com-
missioning and a safe operation of SCHMIDT®Flow sensor SS20.420.
These instructions for use must be read completely and observed care-
fully, before putting the unit into operation.
Any claims under the manufacturer's liability for damage resulting from
non-observance or non-compliance with these instructions will become
void.
Tampering with the device in any way whatsoever - with the exception
of the designated use and the operations described in these instruc-
tions for use - will forfeit any warranty and exclude any liability.
The unit is designed exclusively for the use described below (see chap-
ter 2). In particular, it is not designed for direct or indirect protection of
personal and machinery.
SCHMIDT Technology cannot give any warranty as to its suitability for
certain purpose and cannot be held liable for errors contained in these
instructions for use or for accidental or sequential damage in connec-
tion with the delivery, performance or use of this unit.
Symbols used in this manual
The symbols used in this manual are explained in the following section.
Danger warnings and safety instructions - read carefully!
The non-observance of these instructions may lead to personal
injury or malfunction of the device.
General information
All dimensions are indicated in millimeter.
!

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 4
2 Application Range
The SCHMIDT®Flow sensor SS 20.420 (article number: 538045) is de-
signed for stationary use in cleanrooms, air ducts or air shafts under at-
mospheric pressure conditions and clean environmental conditions. The
sensor measures the flow velocity of the measuring medium as standard
velocity
1
(unit: m/s) relative to standard pressure of 1,013.25 hPa and
standard temperature of 20 °C. The output signal is linear and independ-
ent of pressure and temperature of the medium.
Optionally, the sensor can measure in both directions (see chapter 5).
The decisive characteristics of the product are listed below:
Measuring task
oMeasurement of flow velocity
oDetection of flow direction (bidirectional version)
Application examples
oLaminar-flow monitoring in cleanrooms
oMonitoring of room-to-room overflow
oCooling air monitoring
oFlow measurement in test benches
Only suitable for the use in clean gases.
In particular, the medium to be measured must not contain oils,
residue forming substances or abrasive particles.
When transporting the sensor or when carrying out not approved
cleaning procedures, always place the protective cap on the
head of the probe.
The SCHMIDT®Flow sensor SS 20.420 is designed for the use
inside closed rooms and is not suitable for outdoor use.
1
Corresponds to the actual flow velocity under standard conditions.
!
!
!

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 5
3 Mounting Instructions
The following accessories are available for installation:
Type / art. no.
Drawing
Assembly
Compression
fitting
532160
G1/2
39
SW17
SW27
14 Ø9,2+0,1
- Immersion sensor
- Pipe (typ.)
- Wall
- Screwing into a clamp2
- Material:
Stainless steel 1.4571
Clamp collar PTFE
Wall mounting
flange
520181
- Immersion sensor
- Wall (plain surface)
- To be fixed with:
2 screws M53
- Material:
Stainless steel 1.4404
PTFE
O-ring Viton
Wall mounting
bracket
(an. aluminum)
503895
- Room-to-room overflow
- Wall (plain surface)
- Attachment with:
2 screws M5 x 12
- Material:
Aluminum, anodised
Wall mounting
bracket
(stainless steel)
551740
- Room-to-room overflow
- Wall (plain surface)
- Attachment with:
2 screws M5 x 12
- Material:
Stainless steel 1.4404
Table 1
All mounting fixtures fasten the sensor by means of frictional clamping on
the sensor tube. This enables stepless positioning of the sensor in the
holder both axially in direction of the longitudinal sensor axis (immersion
depth) as well as in rotational direction around the same axis (tilting).
The angle of tilt
4
to flow direction should not exceed ±3° in order to
avoid significant measuring errors (> 1 %).
2
Commercially available welding stud (not included in the delivery) must be welded.
3
Countersunk head (not included in the delivery).
4
Deviation between measuring direction of sensor head and flow direction.
Set screw M4x3
Stainless A4

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 6
Figure 3-1
In inhomogeneous, laminar flow fields (for example a quasi-parabolic
speed profile in a tube), the sensor tip should be positioned at the place
at which the highest speed occurs (adjustment of the immersion depth;
see Figure 3-2) since this point has normally the largest distance to
interfering elements such as boundary surfaces.
If correctly mounted, both compression fitting as well as wall mounting
flange are tight up to a gauge pressure of 500 mbar
5
.
For measurements in media with overpressure, appropriate
safety measures must be taken to prevent unintended dis-
carding of the sensor.
Tube-related flow
Installation in a flow guiding tube is carried out by means of a compression
fitting (532160, see Figure 3-2):
Screw the threaded part of the compression fitting into the welded pipe
union (hexagon AF 27) tightly. Unscrew the spigot nut (AF17) to such
an extent that the sensor probe can be inserted without jamming.
Introduce sensor into compression fitting until the sensor tip is located
in the middle of the tube. Then tighten spigot nut slightly using a fork
wrench AF17 to fix the sensor.
Figure 3-2
5
The screw-in thread of the compression fitting must be sealed, e.g. with teflon tape.
!
Compression fitting
532160

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 7
Align sensor to nominal flow direction (direction of arrow) considering
that immersion depth must be maintained.
The angular deviation should not be greater than 3° refer-
enced to the ideal position. Otherwise measurement accu-
racy may be affected (deviation > 1 %).
Tighten spigot nut by turning the fork wrench (AF17) by a quarter while
maintaining the sensor in position.
To reach the accuracy specified in its data sheet, the SS 20.420 has to be
positioned in a straight pipe and at a place with undisturbed flow profile.
An undisturbed flow profile can be achieved if a sufficiently long distance
in front of the sensor (run-in distance) and behind the sensor (run-out dis-
tance) is held absolutely straight and without disturbances (such as edges,
seams, bends, etc.).
Correct measurements require laminar6flow with as low turbu-
lence as possible.
The design of the run-out distance is also important, since disturbances
do not only act in direction of the airflow but also lead to turbulences op-
posite to flow direction.
L
= Length of whole measuring distance
L1
= Length of run-in distance
L2
= Length of run-out distance
D
= Inner diameter of measuring distance
Figure 3-3
The following Table 2 shows the required straight pipe lengths depending
on the inner tube diameter D and different causes of disturbances.
This table lists the minimum values required in each case. If the listed
straight pipe lengths cannot be achieved, measurement accuracy may be
impaired or additional actions are required like the use of flow rectifiers
7
.
6
The term “laminar” means here an air flow low in turbulence (not according to its physical
definition saying that the Reynolds number is < 2300).
7
E.g., honeycombs made of plastics or ceramics; profile factor may change therefore.
!
!

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 8
Flow obstacle upstream of measuring distance
Minimum distance length of
Run-in (L1)
Run-out (L2)
Light bend (< 90°)
10 x D
5 x D
Reduction,
expansion,
90° bend or
T-junction
15 x D
5 x D
Two 90° bends in
one plane
(2-dimensional)
20 x D
5 x D
Two 90° bends with
3-dimensional
change in direction
35 x D
5 x D
Shut-off valve
45 x D
5 x D
Table 2
When mounting the sensor in a tube with a known cross section area, the
output signal of the flow velocity can be used to calculate the standard
volumetric flow of the medium.
D
Inner diameter of tube [m]
A
Cross section area of tube [m2]
N
w
Flow velocity in the middle of tube [m/s]
N
w
Average flow velocity in tube [m/s]
PF
Profile factor (for tubes with a circular cross section A)
N
V

Standard volumetric flow [m3/s]
SCHMIDT Technology provides on its homepage a convenient calcula-
tion tool to compute flow velocity or volume flow in pipes (circular or rec-
tangle) for all its sensor types and measuring ranges:
www.schmidt-sensors.com
www.schmidttechnology.de
AwV
wPFw
DA
NN
NN




2
4


Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 9
Wall mounting
The wall mounting flange (520181) is designed for installation of the flow
sensor SS 22.420 as an immersion sensor through a wall (e.g. wall of a
flow box). The threaded bush included in the delivery has a base provided
with a plane contact surface and two holes which allow a fast and easy
installation by means of two screws.
All advantages, requirements and installation instructions regarding the
stepless sensor installation are applicable for the compression fitting (see
subchapter: Tube-related flow).
Mounting for measuring room-to-room overflow
A room-to-room overflow sensor is fixed by means of a wall mounting
bracket (503895 in anodized aluminum or 551740 in stainless steel). The
sensor should be placed in flow direction behind the wall opening,
whereas the sensor tip must be located in the middle of the opening (see
Figure 3-4 for an example with 503895).
Figure 3-4
The application of a SS 20.420 with bidirectional measurement
capability allows the detection of backflow and is therefore able
to signalize critical operating conditions.
!
(Wall opening)

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 10
4 Electrical Connection
During electrical installation ensure that no voltage is applied
and inadvertent activation is not possible.
The sensor is equipped with a firmly attached connection cable (pin as-
signment see Table 3).
No.
Designation
Function
Wire colour
1
Power
Operating voltage: +UB
Brown
2
Flow
Velocity signal wN
Green
3
GND
Operating voltage: mass
White
Table 3
The metallic housing of the sensor is indirectly coupled to GND (VDR
8
, in
parallel with 100 nF) and should be connected to an anti-interference po-
tential, e.g. GND (depending on the shielding concept).
The appropriate protection class III (SELV) respective PELV
(EN 50178) has to be considered.
Operating voltage
The SS 20.420 is protected against a polarity reversal of the operating
voltage.
It has a nominal operating voltage range of UB= 12 ... 26.4 VDC.
Only operate sensor in the defined operating voltage range
(12 ... 26.4 VDC).
Undervoltage may result in malfunction. Overvoltage may lead to
irreversible damage to the sensor.
The specifications for the operating voltage are valid for the connection at
the sensor. Voltage drops generated due to line resistances must be con-
sidered by the customer.
Current consumption of the sensor is typical 6 mA, at maximum less than
10 mA (including signal output current).
8
Voltage dependent resistor; breakdown voltage 27 V @ 1 mA
!
!
!

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 11
Analog signal output
The analog output utilizes a voltage interface featuring permanent short-
circuit protection against both rails of the operating voltage UB.
Signal range: 0 ... 10 V
Type: High side driver, load resistance against GND
Minimum load resistance RL: 10 kΩ
Maximum load capacity CL: 1 nF
Maximum short-circuit current: 10 mA
Maximum cable length: 10 m
Wiring:
Figure 4-1
The voltage drop9in the GND wire of the connecting cable (mass
offset) can significantly affect the analog signal of the voltage out-
put.
9
The specific resistance of the lead of the connecting cable (0.14 mm2) is 0.138 /m
(20 °C); at L = 10 m a current of IB,max = 10 mA can cause a voltage drop up to 14 mV.
!

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 12
5 Signalizing
Analog output
The SS 20.420 measures flow speed either in one (unidirectional) or op-
tionally in both directions (bidirectional).
Representation of measuring range and flow direction:
The measuring range (0 … wN,max) of the unidirectional version is
mapped proportionally to the whole signaling range (0 … 10 V; see
Table 4, left column). This direction is defined as the nominal measur-
ing direction and marked with two engraved arrows on the sensor tube.
In case of a bidirectional version (measuring range: -wN,max …+wN,max)
the representation area of the analog signal output is spread symmet-
rically, that means a flow of zero complies with 50 % of the signal range
(= 5 V; see Table 4, right column).
Unidirectional version
Bidirectional version

  
 󰇛
  󰇜  
Table 4
Overflow:
Flow speeds which exceed the positive measuring range are further-
more output in a linear way up to 110 % of the measuring range (end
value + 10 %), to signalize clearly that there is an overflow. For higher
values of flow the output signal remains constant.
Error signaling:
The signal output is set to 0 V.

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 13
6 Startup
Prior to turn on the SCHMIDT®Flow sensor SS 20.420, the following
checks have to be carried out:
Immersion depth of the sensor probe and its alignment to the flow di-
rection.
Tightening of fastening screw of the used mounting accessory.
Correct electrical connection of connecting cable in the field.
Correct operating voltage applied (value and polarity).
The sensor is ready for operation about five seconds after switch-on.
If the sensor has another temperature than the ambient, this time is pro-
longed until the sensor has reached ambient temperature.
In case of faults or other problems during installation, the fault table (see
Table 5) can help to resolve the problem.
If the problems persist, please contact SCHMIDT Technology.

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 14
7 Information on Operation
Sterilization
The SS 20.420 can be sterilized during operation.
Approved disinfectants are alcohol (drying without leaving residues). If too
much cleaning agent is applied to the sensor, the "soiling detection" can
be activated and the analog signal is set to error state (0 V). As soon as
the sensor element is dried, the sensor is automatically reset to its normal
function.
Due to its capillarity, the chamber head gap in the sensor tip can
be filled completely with cleaning agent. In this case, it is possible
that it will take more than one hour until the liquid is evaporated
and the sensor works again without problems. To accelerate the
drying process, the measuring gap can be cleaned carefully by
means of a short compressed air blast or similar methods.
Cleaning of the system
If it is necessary to clean the system in which the sensor is installed, using
another cleaning agent than mentioned above the sensor tip must be pro-
tected against the penetration of inappropriate cleaning agents by means
of the protective cap, which is included in the delivery. This is especially
important for cleaning agents which do not dry without leaving residues or
cleaning processes during which may soil the sensor tip.
Prior to carry out problematic cleaning measures (e.g. using in-
admissible cleaning agents), the protective cap (yellow, included
in delivery) must be placed on the sensor head to protect its sen-
sor element.
See also chapter 8 Service Information, subchapter Cleaning sensor tip.
!
!

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 15
8 Service Informations
Maintenance
A soiled sensor tip may distort the measured value. Therefore, the sensor
tip must be checked for soiling at regular intervals.
If it is soiled or wetted by a liquid, the sensor signal error (0 V) via the
analog output. In this case, clean the sensor as described below.
If the error signal does not disappear after cleaning and drying, the sensor
must be sent in to the manufacturer for repair.
Cleaning sensor tip
If the sensor tip is soiled or dusty, it must be carefully cleaned by means
of compressed air (avoid strong pressure impulses!).
If this procedure is not successful, the sensor tip can be cleaned by im-
mersing and washing it in alcohol, which dries without leaving residues
(e.g. isopropyl alcohol). As soon as the alcohol has been evaporated, the
sensor is again ready for operation.
Do not shake or tap the wet sensor!
Do not try to clean the sensor tip by any type of mechanical
methods. Do not touch the sensor element located in the
chamber head. This may irreversibly damage the sensor.
Do not use strong cleaners, brush or other objects, fluffy
cloths etc. to clean the sensor tip!
Inappropriate cleaning agents may leave residues on the
sensor element and therefore lead to faulty measurements or
result in permanent damage to the sensor element.
If the chamber head gap of the sensor tip is completely filled
with cleaning agent, accelerate the drying process by blowing
it out, if necessary.
!

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 16
Removing malfunctions
The following Table 5 lists possible errors with a description how to detect
them. Furthermore, possible causes and measures to be taken to remove
them are listed.
Error image
Possible cause
Remedy
No output signal
AOut = 0 V
Operating voltage
(not / incorrectly connected)
Check operating voltage and
wiring
Sensor defective
Send in for repair
Error message of sensor
AOut = 0 V,
although there is a flow
Sensor element wetted
Wait until element is dry
Blow out sensor tip
(if possible)
Sensor element soiled
Clean sensor tip
Sensor element defective
Send in for repair
Unexpected values of
analog output
Measured AOut :
Too high / low
Strong noise or drift
Sensor configuration
(measuring range / indica-
tion of direction)
Check order configuration
and measurement settings
Medium to be measured
does not correspond to the
calibration medium
(Standard conditions: Air at
1013.25 hPa and 20 °C)
Check medium parameters
Mounting conditions
(tilting / immersion depth /
distortion)
Check mounting conditions
Irregular flow behaviour
(turbulences / other disturb-
ances)
Check run-in and run-out dis-
tances
Sensor element soiled
Clean sensor top etc.
Operating voltage not OK
(DC / value / stability)
Check operating voltage
Large / fast variations of
pressure and temperature
Check medium parameters
Improper electrical load
Load resistance RL< RL,min
Increase resistance ≥ 10 k
Load capacity CL> CL,max
Reduce capacity ≤ 1 nF
Insert resistor in series to C
L
Table 5

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 17
Transport / dispatch of the sensor
Before transport or dispatch of the SS 20.420, the delivered pro-
tective cap must be put over the sensor head.
Avoid soiling or mechanical stress.
Calibration
If the customer has made no other provisions, we recommend repeating
the calibration at a 12-month interval. To do so, the sensor must be sent
in to the manufacturer.
Spare parts or repair
No spare parts are available, since a repair is only possible at the manu-
facturers. In case of defects, the sensors must be sent in to the supplier
for repair.
When the sensor is used in systems important for operation, we recom-
mend keeping a replacement sensor in stock.
Test certificates and material certificates
Every newly produced sensor is accompanied by a certificate of compli-
ance according to EN 10204-2.1. Material certificates are not available.
Upon request, we shall prepare, at a charge, a factory calibration certifi-
cate, traceable to national standards.
!

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 18
9 Technical Data
Measuring quantity
Normal velocity wNof air based on normal conditions of
20 °C and 1013.25 hPa
Medium to be measured
Clean air or nitrogen; more gases on request
Measuring range
(±) 0 ... 1 / 2.5 / 5 / 10 m/s
Unidirectional or bidirectional
Lower detection limit
(±) 0.05 m/s
Measuring accuracy10
- Standard
- High precision
±(5 % of meas. value +[1 % of end value; min. ± 0.05 m/s])
±(3 % of meas. value +[1 % of end value; min. ± 0.05 m/s])
Repeatability
±2 % of measured value
Response time (t90)
0.2 s
Analogue output
- Type
- Load
Short circuit protected
Voltage (0 ... 10 V)
RL≥ 10 kΩ, CL≤1 nF
Operating voltage
12 ... 26.4 V DC (reverse voltage protected)
Current consumption
Typ. 6 mA (max. 10 mA11)
Humidity range
≤95 % RH (not condensing)
Operating pressure
Atmospheric (700 ... 1,300 hPa)
Mounting tolerance
±3° relative to nominal flow direction
Operating temperature
0 ... +60 °C
Storage temperature
-20 ... +85 °C
Connection cable
Fixed at housing, pigtail12, 3 x 0.14 mm2, 5 m, PVC
Protection class
III (SELV) or PELV (according EN 50178)
Protection type
IP65
Dimensions / material
- Sensor head
- Sensor tube
- Total length of sensor
Ø 9 mm x 10 mm Stainless steel 1.4404
Ø 9 mm x 50 / 100 mm Stainless steel 1.4404
60 / 110 mm
Weight
About 40 g
10
Under reference condition
11
Including signal output current
12
Sheath approx. 50 mm stripped, stranded ends approx. 6 mm stripped and tinned

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 19
10 Declarations of Conformity
SCHMIDT Technology GmbH herewith declares in its sole responsibility,
that the product
SCHMIDTFlow Sensor SS 20.420
Part-No. 538 045
is in compliance with the appropriate
European guidelines and standards
and
UK statutory requirements and designated standards.
The corresponding declarations of conformity can be download from
SCHMIDT®homepage:
www.schmidt-sensors.com
www.schmidttechnology.de

Instructions for Use –SCHMIDT®Flow sensor SS 20.420 Page 20
SCHMIDT Technology GmbH
Feldbergstraße 1
78112 St. Georgen
Germany
Phone [phone] / 899-0
Fax [phone] / 899-101
Email [e-mail]
URL www.schmidt-sensors.com