Schmidt SS 23.400 ATEX 3 User manual

SCHMIDT®Flow Sensor
SS 23.400 ATEX 3
Instructions for Use

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 2
SCHMIDT®Flow Sensor
SS 23.400 ATEX 3
Table of Contents
1Important information.......................................................................3
2Application range.............................................................................5
3Mounting instructions.......................................................................6
4Electrical connection......................................................................13
5Signaling........................................................................................18
6Startup...........................................................................................21
7Information concerning operation..................................................22
8Service information........................................................................23
9Type examination certificate ATEX...............................................25
10 Technical data ...............................................................................26
11 Declaration of conformity...............................................................27
Imprint:
Copyright 2020 SCHMIDT Technology GmbH
All rights reserved
Version: 514622.02G
Subject to modifications

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 3
1 Important information
These instructions for use contain all required information for a fast com-
missioning and safe operation of SCHMIDT®Flow sensor SS 23.400
ATEX 3:
These instructions for use must be read completely and observed
carefully, 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
chapter 2). In particular, it is not designed for direct or indirect protec-
tion of personal and machinery.
SCHMIDT Technology cannot give any warranty as to its suitability
for certain purpose and cannot be held liable for accidental or sequen-
tial damage in connection 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!
Non-observance of these instructions maylead to personal injury
or malfunction of the device.
Risk of explosion - read carefully!
Important instructions for use in areas subject to explosion haz-
ards.
!

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 4
General information
Operate sensor only with original connecting cables from
SCHMIDT Technology (see chapter “4 Electrical connection”).
Use of any other cable makes the ATEX approval null and void.
Only suitable for use in clean gases.
The medium to be measured must not contain oils, residue form-
ing substances or abrasive particles.
When transporting the sensor or carrying out not approved clean-
ing operations, always place the yellow protective cap on the
sensor tip.
All dimensions are given in mm.
!
!

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 5
2 Application range
The SCHMIDT®Flow sensor SS 23.400 ATEX 3 (article number:
513970) is designed for stationary measurements of the flow velocity of
air and gases at atmospheric pressure and under clean ambient condi-
tions.
The sensor is based on the measuring principle of a thermal anemometer
and measures the mass flow of the measuring medium as flow velocity
which is output in a linear way as standard velocity
1
wN (unit: m/s), based
on standard conditions of 1013.25 hPa and 20 °C. Thus, the resulting out-
put signal is independent from the pressure and temperature of the meas-
uring medium.
The essential characteristics of the product are listed below:
Measuring task
oMeasurement of flow velocity
oDetection of flow direction
(bidirectional measurement, optional)
Application examples
oLaminar-flow monitoring in cleanrooms
oMonitoring of room cross-flow
oCooling air monitoring
oFlow measurement in test benches
oDraft monitoring
Use in areas subject to explosion hazards
The device can be installed only in hazardous areas with
gases (G) and in Zone 2.
Note:
Only suitable for use in clean gases.
The medium to be measured must not contain oils, residue
forming substances or abrasive particles.
The SCHMIDT®Flow sensor SS 23.400 ATEX 3 is designed for use in-
side closed rooms and is not suitable for outdoor use.
1
Corresponds to the real velocity under standard conditions mentioned above.
!

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 6
3 Mounting instructions
For installation of the SS 23.400 ATEX 3 the following accessories are
available (see Table 1):
Type / art. no.
Drawing
Assembly
Through bolt
joint
532160
G1/2
39
SW17
SW27
14 Ø9,2+0,1
- Immersion sensor
- Pipe (typ.)
- Wall
- Incorporation in 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 1.4571
PTFE
O-ring Viton
Wall mounting
bracket
(aluminium ano-
dised)
503895
- Room cross-flow
- Wall
- Plain surface
- Attachment with:
2 screws M5 x 12
- Material:
Anodised aluminium
Wall mounting
bracket
(stainless steel)
551740
- Room cross-flow
- Wall
- Plain surface
- Attachment with:
2 screws M5 x 12
- Material:
Stainless steel 1.4404
Table 1
All types of mounting fixtures fasten the sensor by frictional clamping. This
allows stepless positioning of the sensor in the holder concerning its axial
direction (longitudinal sensor axis, immersion depth) and in rotational di-
rection around the same axis (tilting).
2
Commercially available welding stud (not included in delivery) must be welded.
3
Countersunk head, not included in the delivery.
Clamping screw
Set screw M4x3
Stainless A4

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 7
The following points must be observed:
The angle of tilting
4
to the flow direction should not exceed ±5° in order
to avoid significant measuring errors (> 1 %).
In inhomogeneous, laminar flow fields (for example a quasi-parabolic
speed profile in a pipe), the sensor tip should be positioned at a point
with the highest speed (adjustment of the immersion depth) because
this position normally has the largest distance to interfering elements
such as boundary surfaces.
Both the through-bolt joint as well as the wall mounting flange are
pressure-tight up to an overpressure of 500 mbar provided the instal-
lation has been carried out properly
5
.
The customer bears the responsibilityfor securing the sensor
against unintended discarding due to overpressure.
Flow with medium separation
To ensure the enclosure type of protection IP54 observe the fol-
lowing mounting drawing for media-separated installation using
the through-bolt joint or wall mounting flange (see for example
Figure 3-1).
Figure 3-1
4
Deviation between the measurement direction of the sensor head and flow direction.
5
The screw-in thread of the through-bolt joint must be sealed for this purpose, e.g. by
means of a copper seal or teflon tape.
!
Trough-bolt joint
532160

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 8
Pipe-related flow
Installation in a flow-guiding pipe is carried out by means of a through-bolt
joint (532160, see also Figure 3-1):
Screw the threaded part of the through-bolt joint into the pipe union
(hexagon with AF27).
If pressure tightness is required, first, seal the thread (e.g. wrap it
with a teflon tape).
Unscrew the spigot nut (AF17) to such an extent that the sensor can
be inserted without jamming.
Remove the protective cap from the sensor tip and insert the sensor
into the bore of the DG so that its tip is in the middle of the pipe.
Tighten the spigot nut slightly by hand or with a fork wrench (AF17) to
fasten the sensor.
Align the sensor according to the nominal flow direction (direction of
the arrow) while the immersion depth must be maintained.
The angular deviation should not exceed 5° relatively to the
ideal position. Otherwise, the measurement accuracy may be
impaired.
To tighten the spigot nut, turn the fork wrench (AF17) a quarter of a
turn. While doing this hold the sensor to ensure that it remains in po-
sition.
To achieve the accuracy specified in the data sheets, the sensor has to
be positioned in a straight pipe section 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 without disturbances (such as edges,
seams, bends etc.; see Figure 3-2).
Correct measurements require laminar6flow with turbulences as
low as possible.
The design of the run-out distance is also important, since disturbances
do not only act in the direction of the air flow but also lead to turbulences
against the flow direction.
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).
!
!

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 9
L
= Length of entire measuring section
L1
= Length of run-in distance
L2
= Length of run-out distance
D
= Diameter of measuring section
Figure 3-2
The following Table 2 specifies the required straight lengths of the pipe
sections depending on pipe diameter in case of different disturbances.
Flow obstacle upstream of measuring distance
Minimum length of distance
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
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 flowrectifiers
7
.
Under laminar conditions a quasi-parabolic speed profile emerges over
the pipe cross-section, whereas the flow velocity at the pipe walls remains
7
E.g. honeycombs made of plastics or ceramics; profile factor may change there-fore.

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 10
almost zero while reaching its maximum wN in the pipe center (the opti-
mum measuring point). This measuring value can be converted to an av-
erage speed
N
w
which is constant over the pipe cross-section by using a
correction factor, the so-called profile factor PF. This profile factor de-
pends on the pipe diameter
8
(details see flow calculator).
Thus, it is possible to calculate the standard volumetric flow of the medium
using the measured standard flow velocity in a pipe with known inner di-
ameter:
SCHMIDT Technology provides a convenient calculation tool to compute
flow velocity or volume flow in pipes (circular or rectangle) for all its sensor
types and measuring ranges on its homepage:
www.schmidt-sensors.com
Wall mounting
The wall mounting flange (520181) is designed for the installation of the
flow sensor SS 23.400 ATEX 3 as an immersion sensor through a (locally
even) wall (e.g. wall of a flow box). In general, the flange differs from the
through-bolt joint only by the type of fastening on the wall. The threaded
bush included in the delivery has a broadened base provided with a plane
contact surface and two holes that allow a fast and easy installation by
means of two screws.
Apart from that all advantages, requirements and installation instructions
for the through-bolt joint regarding the stepless sensor installation apply
(see subchapter: “Pipe-related flow”).
8
Both inner air friction as well as obstruction caused by the sensor is responsible.
D
Inner diameter of pipe [m]
A
Cross section area of pipe [m2]
N
w
Peak flow velocity in the middle of pipe [m/s]
N
w
Average flow velocity in the pipe [m/s]
PF
Profile factor (for pipes with circular cross-section)
EF
Measuring unit factor (conversion to non-SI units)
N
V

Standard volumetric flow [m³/s]
EFAwV
wPFw
DA
NN
NN




2
4


Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 11
Mounting as a cross-flow sensor
The mounting as a cross-flow sensor is carried out by means of a wall
mounting bracket (503895, made of anodized aluminium or 551740, made
of stainless steel). The sensor should be placed in flow direction behind
the wall opening, its tip must be located in the middle of the opening.
To ensure the type of protection IP54, the following mounting
drawing must be observed (see Figure 3-3 for exemplary use of
503895).
Figure 3-3
The application of a SS 23.400 ATEX 3 with bidirectional meas-
urement capability allows the detection of backflow and is there-
fore able to signalize critical operating conditions.
ATEX Installation regulation
The sensor must be installed properly in the following order:
Mechanical installation
See previous subchapter
Connection of the equipotential bonding
The metallic enclosure of the sensor must have electrical con-
nection to a ground conductor or an equipotential bonding
conductor according to EN 60079-0 chapter 15. The expres-
sion „electrical connection“ does not always require a conduc-
tor; for example, the equipotential bonding can also be imple-
mented by means of a grounded holder which is in permanent
!
Wall mounting flange
(503895)
Connection
cable
(Wall opening)
Wall mounting bracket
(503895)

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 12
electric, low-resistance contact with the sensors enclosure9.
Whenusing a cable the locking screw at the plug-in connector
of the sensor is designed for this purpose.
In general the following applies for the grounding:
The external ground connection on the enclosure mustbe
connected to the equipotential bonding of the Exarea with
low resistance.
No equipotential current must flow between the Ex areas
and non-hazardous areas.
Minimum cable cross-section: 1 x 4 mm2
The screw must be tightened firmly at the terminal so that
the conductor cannot be loosened or twisted.
Connecting the cable
Connect the shield meshwork (in the non-hazardous
area) to the ground potential on a large surface.
No equipotential current must flow between the Ex areas
and non-hazardous areas.
Labeling
The rating plate for labeling according to the standards is fixed
at the sensor by means of a wire loop.
If required, the customer can attach this plate at another place
provided that it can be clearly assigned to the sensor and is
legible and undetachably. Examples are:
Mounting it directly at the sensor by means of machine
screws through the fixing hole.
Mounting it undetachably onto the wall according to
EN 60079-0, chapter 29.6. The side with the warning note
"Do not disconnect under voltage" must remain visible.
9
The types of holders supplied by SCHMIDT®are not suitable for this purpose.

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 13
4 Electrical connection
Plug-in connector
The sensor features a firmly integrated plug-in connector:
Number of connection pins: 7 (plus shield connection on the metallic housing)
Type: Male
Fixation of connecting cable: Screw M9 (spigot nut on the cable)
Protection type: IP67 (with screwed cable)
Model: Binder, series 712
View at plug-in connector
of sensor
WARNING!
DO NOT DISCONNECT CONNECTING
CABLE AND SENSOR WHEN THEY ARE
UNDER VOLTAGE!
Figure 4-1
For pin assignment of the plug-in connector see Table 3.
Pin
Designation
Function
Wire color
1
Power
Operating voltage : +UB
white
2
TXD
Do not connect
brown
3
RXD
Do not connect
green
4
OC1
Switching output 1: Direction / threshold
yellow
5
OC2
Switching output 2: Switch threshold
gray
6
Analog
Velocity signal
Pink
7
Ground
Operating voltage : Mass
Blue
Shield
Electromechanical shielding
Shield meshwork
Table 3
All signals use as electric reference the potential GND.
The cable shield is connected to the metallic housings of the plug-in con-
nector and the sensor enclosure and must be connected to an anti-inter-
ference potential, e.g. ground (depending on the shielding concept).
The wire color mentioned in Table 3 is applicable for the use of SCHMIDT®
cables with material Nos. 535279
10
and 565072.
The ATEX approval is valid only when using the cables of
SCHMIDT®mentioned above with material nos. 53527910 and
565072.
10
Also allowed are the formerly orderable cable with material no. 505911-x (x = 1 / 2 / 3).

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 14
Electrical assembly
Prior to carry out operations such as assembly, electrical connection, re-
pair work or loosening a plug-in connector, make sure that:
The system is disconnected from the mains.
The system cannot be switched on inadvertently.
The appropriate protection class PELV has to be considered.
The following safety measures must be observed in hazardous
areas:
Check if the device category corresponds to the specified
zones.
Check if the operation approval from the operator is availa-
ble.
Check if there is an explosive atmosphere available.
Compliance with the applicable regulations and the entire rel-
evant documentation for this device.
Operating voltage
The SS 23.400 ATEX 3 is protected against polarity reversal of the oper-
ating voltage.
It has a nominal voltage range of UB= 12 ... 26.4 VDC.
Only operate sensor within the defined range of operating voltage
(12 ... 26.4 VDC).
Undervoltage may result in malfunction. Overvoltage may lead to
irreversible damage to the sensor.
Specifications for the operating voltage apply for the connection of the
sensor. Voltage drops generated due to line resistances must be consid-
ered by the customer.
The current consumption of the sensor is 35 mA typically, peak current is
150 mA (incl. all signal output currents at their maximum).
!
!

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 15
Analog output
The analog output is protected against a short circuit towards the operat-
ing voltage or the mass.
It is available in two basic versions which differ in the representation range
(final value, directionality):
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 output:
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 drop11 in the GND wire of the connecting cable
(mass offset) can significantly affect the analog signal at the volt-
age output.
11
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 of up to 240 mV.
!

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 16
Switching outputs
The sensor is equipped with two current limited and short-circuit resistant
switching outputs with the 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
12
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 (recommended)
Wiring:
The individual switching outputs can be used as follows:
Direct driving of a resistive or inductive load (e.g. LED or relays) with
a maximum current consumption of 55 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:
    
12
Measuring resistor and switching transistor; additional leakage current of the TVS diode
connected in parallel (UOC ≈ US,max): < 100µA

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 17
If the maximum current is almost reached, the emitter resistance gen-
erates an inverse feedback holding the current ISvirtually constant
while the voltage drop over the switching transistor (from UOC ≈2.6 V)
rises significantly (analog current limiting).
Regarding this borderline case, the minimum allowed (static) load re-
sistance RL,min at an actually active switching voltage UScan be calcu-
lated
13
:
  

Example:
At switching voltage of US,max = 26.4 V is RL,min = 476 .
If the load resistance is too low (e.g. a short circuit), a digital short-
circuit protection comes in effect. It switches the output on and off (im-
pulse length of switch through is approx. 1 ms, switch-off break approx.
300 ms) until the cause of the faulty switching is eliminated.
An inrush current due to a high capacitive load can trigger the
quick-reacting short-circuit protection (permanent) although
the static current requirement would be below the maximum
current IS,max .
An additional resistance connected in series to the load ca-
pacity can eliminate the problem.
Each switching output is protected against voltage peaks by an uni-
polar TVS diode
14
. Positive voltage impulses, e.g. due to ESD sparks
or an inductive load, are limited to approx. 30 V at the connecting pin,
negative impulses are short-circuited against GND (conducting-state
voltage of a diode).
13
The basic current of the switching transistor is negligible.
14
Transient Voltage Suppressor Diode

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 18
5 Signaling
Analog output
The following is applicable for all output versions:
Representation of the measuring range:
The measuring range of the flow velocity (0 … wN,max or ±wN,max) is
mapped in a linear way to the signaling range of the associated analog
output (see Table 4).
Voltage mode (U)
Current mode (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 (unidi-
rectional) or in both directions (bidirectional). For indication of direction,
there are different possibilities mostly in combination with switching
output OC1 (see also next subchapter: “Switching outputs”).
In an unidirectional version (see Figure 5-1), the switching output OC1
is used to signalize clearly a zero flow (factory setting
16
). 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 the nominal measuring direction (defined as positive) of the sensor tip.
16
OC1 can be configured optionally to any threshold value within measuring range.

Instructions for Use –SCHMIDT®Flow Sensor SS 23.400 ATEX 3 Page 19
Figure 5-1
To distinguish between positive and negative flow direction, bidirec-
tional versions use the switching output OC1 (see Figure 5-2) or the
representation area of the analog signal output is halved, that means
that zero flow is located at 50 % of the signaling range (see Figure
5-3).
Figure 5-2 Figure 5-3
Error signaling:
The voltage interface (0 ... 10 V) is set to 0 V.
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 23.400 ATEX 3 Page 20
Switching outputs
The switching outputs are used as threshold value switches, i.e. they
change their switching condition while in normal measuring operation as
soon as the measured flow velocity exceeds or falls below the respective
threshold value.
Switching hysteresis:
The threshold value is symmetrically superimposed by a fixed hyste-
resis. 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 defined procedure (from "locked" to "conduc-
tive" or vice versa).
Both switching outputs are configured in factory to a positive polarity
that means that the previously conductive transistor locks if the switch-
ing threshold is exceeded (and, in connection with the switching load
RL, switches to a positive voltage level of US).
Switching polarity is configurable by ordering.
Configuration OC1:
If the analog indication area of the bidirectional version corresponds
to the amount of the measuring range, OC 1 is used to signalize the
direction (see Figure 5-2).
Otherwise it is used as a freely programmable threshold switch that is
set in factory to a threshold value of 0 m/s.
Configuration OC2:
OC2 can generally be used as a freely programmable threshold switch
and per default the middle of the positive measuring range is consid-
ered as the threshold value.
Error messaging:
Both switching outputs are conducting independently of the configured
switching polarity.