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.
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!
!

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.
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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
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