Schmidt SS 20.400 User manual

SCHMIDT®Flow Sensor
SS 20.400
Instructions for Use

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 2
SCHMIDT®Flow Sensor SS 20.400
Table of Contents
1Important Information ......................................................................3
2Application Range ...........................................................................4
3Mounting Instructions ......................................................................5
4Electrical Connection.....................................................................10
5Signalizing .....................................................................................15
6Startup...........................................................................................18
7Information on Continuous Operation ...........................................18
8Service Information........................................................................19
9Technical Data...............................................................................22
10 Declarations of Conformity............................................................23
Imprint:
Copyright 2021 SCHMIDT Technology GmbH
All rights reserved
Revision: 504301.02G
Errors and technical modifications subject to change

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 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 sensors of the
SS20.400 type.
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
In the following section, all the symbols used in this manual are explained.
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 mm.
!

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 4
2 Application Range
The SCHMIDT®Flow sensor SS 20.400 (article number: 518210) is de-
signed for stationary use in clean rooms, air ducts or air shafts under at-
mospheric pressure conditions and clean environmental conditions.
The sensor measures flow velocity of the measuring medium as standard
velocity
1
wN(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 is able to measure 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 cross-flow
oCooling air monitoring
oFlow measurement in test benches
Only suitable for 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 measures, always place the protective cap on the sen-
sor.
The SCHMIDT®Flow sensor SS 20.400 is designed for applica-
tions inside closed rooms and is not suitable for outdoor use.
1
Corresponds to the actual velocity under standard conditions.
!
!
!

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 5
3 Mounting Instructions
For installation the following accessories are available:
Type / art. no.
Drawing
Assembly
Compressing
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)
- Attachment with:
2 screws M53
- Material:
Stainless steel 1.4404
PTFE
O-ring Viton
Wall mounting
bracket
(an. Aluminium)
503895
- Room-to-room overflow
- Wall (plain surface)
- Attachment with:
2 screws M5 x 12
- Material:
Aluminium, 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 ±5° in order to
avoid significant measuring errors (> 1 %).
2
Commercially available welding stud (not included in delivery) must be welded.
3
Countersunk head, not included in the delivery.
4
Deviation between measuring direction of sensor head and flow direction.
Clamping screw
Set screw M4x3
Stainless A4

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 6
In inhomogeneous, laminar flow fields (e.g. 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 3-1) since this point has normally the largest distance to
interfering elements such as boundary surfaces.
If correctly mounted, both the compression fitting and the wall mounting
flange are tight up to a gauge pressure of 500 mbar
5
.
The customer himself must ensure that the sensor is protected
against an unintentional pressing out caused by the overpres-
sure.
Tube-related flow
Installation in a flow guiding tube is carried out by means of a compression
fitting (532160, see Figure 3-1):
Screw the threaded part of the compression fitting into the pipe union
(hexagon AF 27). Unscrew the spigot nut (AF17) to such an extent that
the sensor can be inserted without jamming.
Introduce sensor into the compression fitting until its tip is located in
the middle of the tube. Then tighten the spigot nut slightly using the
fork wrench AF17 to fix the sensor.
Align sensor to nominal flow direction (direction of arrow) considering
that immersion depth must be maintained.
The angular deviation should not be greater than 5° refer-
enced to the ideal direction of the gaseous flow. Otherwise
measurement accuracy may be affected (deviation > 1 %).
Tighten spigot nut by turning the fork wrench (AF17) by a quarter while
maintaining the sensor in position.
Figure 3-1
5
The screw-in thread of the compression fitting must be sealed, e.g. with a teflon tape.
!
!
Threaded part
532160

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 7
To reach the accuracy specified in its data sheets, the SS 20.400 has to
be positioned in a straight conduit 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 distance) 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 air flow but also lead to turbulences
opposite 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 3-2
The following Table 2 shows the required straight conduit lengths depend-
ing on tube diameter and different disturbances.
This table lists the minimum values required in each case. If the listed
straight conduit lengths cannot be achieved, measurement accuracy may
be impaired or additional actions are required like the use of flow rectifi-
ers
7
.
6
Here the term “laminar” means 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 20.400 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
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:
AwV
wPFw
DA
NN
NN




2
4

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 or www.schmidttechnology.de
D
Inner diameter of pipe [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]

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 9
Wall mounting
The wall mounting flange (520181) is designed for installation of the sen-
sor SS 20.400 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 instal-
lation 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 made of anodized aluminium or 551740 made of stain-
less 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 open-
ing (see Figure 3-3 for exemplary use of 503895).
Figure 3-3
The application of a SS 20.400 with bidirectional measurement
capability allows the detection of backflow and is therefore able
to signalize critical operating conditions.
!
Wall opening
Setscrew M5
For fixation of sensor
Cylinder screw M5
Internal hexagon (2x)
Flow

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 10
4 Electrical Connection
Plug-in connector
The Flow Sensor SS 20.400 is equipped with a plug-in connector which
is firmly integrated in the housing. The connector has the following data:
Number of connection pins: 7 (plus shield connection on the metallic housing)
Type: Male
Fixation of connecting cable: Screw M9 (on cable)
Protection type: IP67 (with properly attached cable)
Model: Binder, series 712
Pin numbering:
Figure 4-1
The pin assignment of the plug-in connector can be found in Table 3.
Pin
Designation
Function
Wire colour
1
Power
Operating voltage : +UB
White
2
TXD
Do not connect8
Brown
3
RXD
Do not connect8
Green
4
OC1
Switching output 1: Direction or threshold
Yellow
5
OC2
Switching output 2: Threshold
Grey
6
Analogue
Velocity signal wN
Pink
7
GND
Operating voltage : Mass
Blue
Shield
Electromechanical shielding
Shield meshwork
Table 3
All signals use GND as electric reference potential.
The wire colours mentioned in Table 3 are applicable for the use of a
SCHMIDT®cable (article no.: 505911-4, 535279 and 535281).
8
Usable with the obsolete Programming Interface (505960).
View on connector of sensor

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 11
Electrical assembly
During electrical installation ensure that no voltage is applied and
inadvertent activation is not possible.
The cable shield is electrically connected to the metallic housings of the
plug-in connector and the sensor which are coupled to GND (VDR
9
, in
parallel with 100 nF). The shield and / or the housing should be connected
to an anti-interference potential, e.g. earth (depending on the shielding
concept).
The appropriate protection class III (SELV) respective PELV
(EN 50178) has to be considered.
Operating voltage
The SS 20.400 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 operating voltage are valid for the connection at the
sensor. Voltage drops generated due to line resistances must be consid-
ered by the customer.
Current consumption of the sensor is typ. 35 mA, at maximum 150 mA
(including all maximal signal output currents).
9
Voltage dependent resistor; breakdown voltage 27 V @ 1 mA
!
!
!

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 12
Analog signal output
The analog output is protected against a short circuit towards both rails.
It is available in two basic versions which differ in the representation range
(signal interval, bipolarity) additionally (see Table 4):
Current interface:
Signal range: 4 ... 20 mA
Type: High side driver, load resistance against GND
Maximum load resistance RL: 300 Ω
Maximum load capacity CL: 100 nF
Maximum cable length: 100 m
Wiring:
Voltage interface:
Signal range: 0 ... 10 V
Type: High side driver, load resistance against GND
Minimum load resistance RL: 10 kΩ
Maximum load capacity CL: 10 nF
Maximum short-circuit current: 25 mA
Maximum cable length: 10 m (recommended)
Wiring:
The voltage drop in the GND wire of the connecting cable (mass
offset10) can significantly affect the analog signal of the voltage
output.
10
The specific resistance of the lead of the nominal cable (0.14 mm2) is 0.138 /m (20 °C);
at L = 10 m a current of IB,max = 150 mA can cause a voltage drop up to 240 mV.
!

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 13
Switching outputs
The sensor is equipped with two current limited and short-circuit protected
switching outputs with following technical data:
Type: Low side driver, open collector
Maximum switching voltage US,max: 26.4 VDC
Maximum switching current IS,max: 55 mA (typ. 50 mA)
Maximum off-state resistance ROff: 1.5 MΩ
11
Minimum load resistance RL, min: Depending on switching voltage US (see below)
Maximum load capacity CL: Depending on switching current IS(see below)
Maximum cable length: 100 m
Wiring:
Each switching output can be used as follows:
Direct driving of ohmic or inductive loads (e.g. LED or relay) with a
maximum current consumption of 50 mA.
Direct activation of digital inputs with (integrated) pull-up resistor RL
(e.g. PLC input).
Due to the internal measuring resistorwhich is connected in parallel to
the transistor, the switching stage has a comparatively low off-state re-
sistance of 1.5 M. This should be taken into account in case of a (high
resistance) pull-up resistor RL. For a digital evaluation, it is recommended
to choose a value of RL< 167 kso as to achieve an active high level
(locked transistor) which is 10 % below switching voltage USor higher.
Because of its open collector design, the switching voltage USis independ-
ent of the operating voltage UBof the sensor. Thereby it does not behave
like an ideal switch (in particular in combination with the protective mech-
anism) but exhibits in conductive condition a drop voltage UOC with follow-
ing behaviour:
Well below the maximum current IS,max, the open circuit voltage UOC
results from voltage drop via the emitter resistance REplus saturation
voltage over the collector emitter path of the switching transistor:
    
11
Measuring resistor and switching transistor; additional leakage current of the TVS diode
connected in parallel (UOC ≈ US,max): < 100 µA

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 14
If maximum current is almost reached, the emitter resistance locks the
switching transistor by an inverse feedback so that the voltage drop
over the transistor (from UOC ≈ 2.6 V) rises significantly while the cur-
rent remains constant (analog current limiting). From this borderline
case, the minimum allowed (static) load resistance RL,min at an defined
voltage UScan be calculated
12
:
 󰇟󰇠 
 
Example:
RL,min = 476 at maximum switching voltage US,max = 26.4 V.
If the load resistance is too low (e.g. short-circuit), a digital short-circuit
protection will become active which clocks the switching output (switch
impulse
13
of approx. 1 ms duration, pause of approx. 300 ms with
locked transistor) until the cause of the faulty switching is eliminated.
In case of a high capacitive load CL, the inrush current impulse
may trigger the quick-reacting short-circuit protection (perma-
nently) although the static current requirement is below the
maximum current IS,max. An additional resistor connected in
series to CLcan eliminate the problem.
Each switching output is protected against voltage peaks by an unipo-
lar TVS diode
14
(see wiring diagram). Positive voltage impulses (e.g.
due to an inductive load) are limited to approx. 30 V, negative impulses
are short-circuited against GND (conducting-state voltage of a diode).
12
Basic current of the switching transistor can be neglected.
13
Transistor conducting
14
Transient Voltage Suppressor diode

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 15
5 Signalizing
Analog output
The following is valid for all output versions of the SS 20.400:
Representation of measuring range:
The measuring range of flow velocity (0 … wN,max or |±wN,max|) is
mapped in a linear way to the signaling range of the used analog output
type (see Table 4).
Voltage interface (U)
Current interface (I)

  

  󰇛  󰇜
Table 4
Overflow:
Flow speeds which exceed the measuring range are furthermore out-
put 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.
Indication of flow direction
15
:
Depending on its type, the sensor measures flow only in one (unidirec-
tional) or in both directions (bidirectional).
In an unidirectional version (see Figure 5-1), the switching output OC1
(factory setting)
16
is used to signalize explicit a zero flow. The output
transistor locks if the flow is higher than 0 m/s and conducts if it is lower
or equal to 0 m/s.
15
Related to nominal measuring direction (defined as positive) of the sensor head.
16
OC1 can be configured optionally to any threshold value within measuring range.

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 16
Figure 5-1
To distinguish between positive and negative flow direction, bidirec-
tional versions use either switching output OC1 (see Figure 5-2) or the
representation area of the analog signal output is halved, that means
zero flow is defined at 50 % of the signalling range (see Figure 5-3).
Figure 5-2 Figure 5-3
Error signaling:
The voltage interface (0 … 10 V) is set to zero.
The current interface (4 … 20 mA) signalizes 2 mA.
Response time (damping of measured values):
By default the response time of flow measurement is 1 s.
Optionally it could be configured in the range of 0.01 … 10 s by order.

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 17
Switching outputs
Both switching outputs are used as threshold value switches which means
they change their switching condition during normal measuring operation
as soon as the measured flow velocity exceeds or falls below the adjusted
value.
Switching hysteresis:
The threshold value is symmetrically superimposed by a fixed hystere-
sis. The hysteresis width is 5 % of the threshold value (but at least
0.05 m/s) and is not configurable.
Switching polarity:
The switching polarity is defined as the change in direction of the
switching state during a certain procedure (from "transistor locked" to
"transistor conductive" or vice versa).
Both switching outputs are configured by factory with positive polarity,
which means that a previously conducting transistor locks if the switch-
ing threshold is exceeded (and, in connection with the switching load,
switches to a positive voltage level of US).
Switching polarity is configurable by ordering.
Configuration OC1:
If the analogue indication area of the bidirectional version corresponds
to the absolute value of the measuring range, OC 1 is used to signalize
the direction (see Figure 5-2).
Otherwise it is used as an optionally programmable threshold switch
that is set to a threshold value of 0 m/s by factory.
Configuration OC2:
OC2 can generally be used as a freely programmable threshold switch
(ordering). By default the middle of the positive measuring range is
considered as the threshold value.
Error signaling:
Both switching outputs are conducting independent of their configured
switching polarity.

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 18
6 Startup
Prior to turn on the SCHMIDT®Flow sensor SS 20.400, the following
checks have to be carried out:
Correct connection of connecting cable in the field.
Tightness between sensor connector and connecting cable (flat seal
must be correctly inserted in the female cable connector).
Tight fit of the spigot nut on connecting cable connector.
The sensor is ready for operation about five seconds after switch-on.
If the sensor has another temperature than it’s 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 (Table
5) can help to resolve the problem.
If the problems persist, please contact SCHMIDT Technology.
7 Information on Continuous Operation
Sterilization
The SS 20.400 can be sterilized during operation.
Approved disinfectants are alcohol (drying without leaving residues) and
hydrogen peroxide. 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 or 2 mA). 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 other cleaning agents are used than mentioned above, the sensor tip
must be protected by means of the protective cap included in the delivery.
This is especially important for cleaning agents with dried residues or
cleaning processes during which dirt may come into 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 of the sy-
stem.
!
!

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 19
8 Service Information
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 signals an error via the analog
output (0 V or 2 mA). In this case, clean 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, brushes or other objects like
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 blow-
ing it out, if necessary.
!

Instructions for Use –SCHMIDT®Flow Sensor SS 20.400 Page 20
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 signals
OC1/2 locked
AOut = 0 V / 0 mA
Operating voltage
(too low; not / incorrectly
connected)
Check operating voltage and
wiring
Sensor defective
Send in for repair
Error message of
sensor
OC1/2 conducting
AOut = 0 V / 2 mA
although there is flow
Sensor element wetted
Wait until sensor 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 / drift
Sensor configuration
(Measuring range / direction;
output type)
Check order configuration and
measurement settings
Medium to be measured does
not correspond to calibration
medium
Check medium parameters
(standard medium: Air at
1013.25 hPa and 20 °C)
Mounting conditions
(tilting / immersion depth)
Check mounting conditions
Irregular flow conditions
(turbulences / other disturb-
ances)
Check run-in and -out distance
Increase damping of measured
flow velocity
Sensor element soiled
Clean sensor tip
Operating voltage
(stability / value)
Check operating voltage
Large / fast variations of
pressure and temperature
Check medium parameters
Unexpected values of
switching outputs
Configuration
Check configuration
Faulty wiring
Check wiring
Digital short-circuit protection
active
Load resistance too small
(increase RL> RL,min)
Reduce load capacity CL
Insert resistor in series to C
L
Table 5