Schmidt SS 20.250 User manual

SCHMIDT®Flow Sensor
SS 20.250
Instructions for Use

Instructions for Use –SCHMIDT®Flow Sensor SS 20.250 Seite 2
SCHMIDT®Flow Sensor SS 20.250
Table of Contents
1Important Information ......................................................................3
2Application range.............................................................................4
3Mounting instructions.......................................................................4
4Electrical connection......................................................................10
5Signalizations ................................................................................12
6Startup...........................................................................................14
7Information concerning operation..................................................14
8Service information........................................................................15
9Technical data ...............................................................................18
10 Declarations of conformity.............................................................19
Imprint:
Copyright 2021 SCHMIDT Technology GmbH
Alle rights reserved
Version: 529070.02D
Subject to modifications

Instructions for Use –SCHMIDT®Flow Sensor SS 20.250 Seite 3
1 Important Information
The instructions for use contain all required information for a fast commis-
sioning and a safe operation of SCHMIDT®flow sensors:
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 ornon-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 (refer to
chapter 2). In particular, it is not designed for direct or indirect protec-
tion of personal or 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 may lead to injury of the
personnel or malfunction of the device.
General note
All dimensions are indicated in mm.
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Instructions for Use –SCHMIDT®Flow Sensor SS 20.250 Seite 4
2 Application range
The SCHMIDT®Flow Sensor SS 20.250 (article number: 526 340) is de-
signed for stationary measurement of the flow velocity as well as the tem-
perature of air and gas at atmospheric pressure conditions.
The sensor is based on the measuring principle of a thermal anemometer.
It measures the mass flow of the measuring medium as flow velocity which
is output in a linear way as standard velocity
1
wNbased on standard con-
ditions of 1013.25 hPa and 20 °C. Thus, the resulting output signal is in-
dependent from pressure and temperature of the medium to be measured.
The sensor is designed for the use inside closed rooms and is not suitable
for outdoor use.
When using the sensor outdoors, it must be protected against
direct exposure to the weather.
3 Mounting instructions
General information on handling
The flow sensor SS 20.250 is a sensitive measuring instrument. There-
fore, avoid applying mechanical force onto the sensor tip.
The head of the sensor probe can be damaged irreversibly due
to mechanical loads.
Leave the protective cap during mounting as long as possible
attached and handle the sensor with care.
Flow characteristics
To avoid any distortion of the measurement results, appropriate installa-
tion conditions must be guaranteed to ensure that the gas flow is supplied
to the sensor in a quiet (low in turbulence) state. The corresponding
measures depend on the flow-determining system properties (pipe, flow
box, outdoor environment etc.), they are described in the following sub-
chapters for different mounting variants.
Correct measurements require a (laminar) flow low in turbulence.
Because the sensor has to measure the temperature of the medium also,
the temperature measuring sleeve must be in direct contact with the
measured medium. That means that a minimum immersion depth (MID)
of 58 mm is required (see Figure 3-1).
1
Corresponds to the actual velocity under standard conditions.
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Instructions for Use –SCHMIDT®Flow Sensor SS 20.250 Seite 5
Figure 3-1
Installation in pipes or channels
The central installation of the sensor over the pipe cross-section must be
realized on a point where the flow is quiet. The simplest method
2
for ob-
taining a quiet flow is to provide a sufficiently long distance in front of the
sensor (run-in distance) and behind the sensor (run-out distance) straight
without disturbances (such as edges, seams, bend etc., refer to installa-
tion drawing Figure 3-2).
L
Length of entire measuring distance
L1
Length of run-in distance
L2
Length of run-out distance
D
Inner diameter of measuring distance
Figure 3-2
The required abatement distances (in relation to the pipe’s inner diameter
D) in case of different fault causes are listed in Table 1.
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 ot 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 (3-dimensional change in direction)
35 x D
5 x D
Shut-off valve
45 x D
5 x D
Table 1
This table lists the minimum values required in each case. If the listed
straight conduit lengths cannot be achieved, the measurement accuracy
may be impaired.
Under the conditions mentioned above, a flattened, parabolic velocity pro-
file is produced over the pipe cross-section which reaches its maximum
2
Alternatively flow rectifiers, e.g. honeycomb ceramics, can be used.
L1
L2
L
D
Temperature measuring sleeve
MID

Instructions for Use –SCHMIDT®Flow Sensor SS 20.250 Seite 6
wNin the middle of the pipe (optimum measuring point). This measuring
value can be converted to an average flow velocity
N
w
constant over the
cross-section by means of a so called profile factor PF. This profile factor
depends on the pipe diameter and is shown in Table 2.
Thus, it is possible to calculate the standard volumetric flow using the
measured standard flow velocity in a pipe with known inner diameter:
3600
42



AwV
wPFw
DA
NN
NN


PF
Tube Ø
Measuring range of volumetric flow [m3/h]
Inside
Outside
for sensor measuring range
[mm]
[mm]
1 m/s
2.5 m/s
10 m/s
20 m/s
0.710
70.3
76.1
10
25
99
198
0.720
82.5
88.9
14
35
139
277
0.740
100.8
108.0
21
53
213
425
0.760
125.0
133.0
34
84
336
672
0.795
150.0
159.0
51
126
506
1,012
0.820
182.5
193.7
77
193
772
1,544
0.840
206.5
219.1
101
253
1,013
2,026
0.845
309.7
323.9
229
573
2,292
4,583
0.850
631.6
660.0
959
2,397
9,587
19,175
Table 2
SCHMIDT Technology provides a convenient calculation tool to compute
flow velocity or volume flow in pipes (circular or rectangular) for all its sen-
sor types and measuring ranges on its homepage.
www.schmidt-sensors.com or www.schmidttechnology.de
Since the situation is similar to that in a pipe, the volumetric flow in a
square chamber can be calculated in the same way, i.e. by equating the
hydraulic diameters of both cross-section forms (see Figure 3-3). The re-
sult for a rectangle is a “diameter” DRequivalent to a circular pipe:
D
Inner diameter of pipe [m]
A
Cross-section area of pipe [m2]
N
w
Standard flow velocity in pipe centre [m/s]
N
w
Average standard flow velocity in tube [m/s]
PF
Profile factor (for pipes with circular cross-sections)
N
V

Standard volumetric flow [m3/h]

Instructions for Use –SCHMIDT®Flow Sensor SS 20.250 Seite 7
bK: Width of rectangular channel
hK: Height of rectangular channel
DR: Equivalent pipe diameter
hb hb
DR

2
Figure 3-3
According to this the volumetric flow in a chamber is calculated:
N
KK
KK
N
RNN
NN
KK
KK
R
KK
KK
RR
w
hb hb
PFV
AwV
wPFw
hb hb
A
hb hb
DA




































2
2
2
22
44





bK / hK
Width / height of square chamber [m]
DR
Inner diameter of equivalent pipe [m]
AR
Cross-section area of equivalent pipe [m2]
N
w
Flow velocity in the middle of duct / pipe [m/s]
N
w
Average flow velocity in equivalent pipe [m/s]
PF
Profile factor of pipe3with inner diameter DR
N
V

Standard volumetric flow [m³/s]
Wall installation
In general there are two options available for sensor installation on or (di-
rectly) in a wall:
Installation with a flange
SCHMIDT Technology offers two types of flanges.
55
20
38
5,8
Mounting flange 301048
Wall mounting flange 520181
Figure 3-4
The simple mounting flange (see Figure 3-4, left side) fixes the sensor by
means of a locking screw and is not pressure-tight.
The wall mounting flange (Figure 3-4, right), suitable for clean rooms, is
pressure tight up to 500 mbar, made of stainless steel and uses an O-ring
3
The profile factors are equal for both cross-section forms.
301048

Instructions for Use –SCHMIDT®Flow Sensor SS 20.250 Seite 8
on the contact surface to separates the medium to be measured from the
environment.
Assembly:
Drill a bushing bore with 10 … 12 mm diameter in the wall.
Align and drill bore pattern for fastening screws according to the re-
quired position of the locking screw (mounting flange 301048) or
mounting plate (wall mounting flange 520181).
Screw down the flange.
Remove protective cap and insert sensor probe carefully in coaxial di-
rection into flange.
Adjust immersion depth of the probe and fasten sensor by means of
the locking screw (mounting flange 301046) or lock nut (wall mounting
flange 520181).
Mounting with compression fitting
SCHMIDT Technology offers two compression fittings that differ in mate-
rial (brass or stainless steel; for details refer to subchapter Accessories).
Figure 3-5
L
Sensor length [mm]
DA
Outer diameter of the pipe [mm]
SL
Length of the weld-in sleeve [mm]
E
Sensor tube setting length [mm]
AL
Projecting length [mm]
MID
Minimum immersion depth [mm]
The compression fittings are mounted using their external thread G½. Nor-
mally, a clamp with internal thread G½ resp. Rp½ (for details refer to sub-
chapter Accessories) is welded as a connecting piece onto the bore in the
medium-transporting system wall and the fitting is screwed in.
The further assembly is carried out as described in the previous subchap-
ter.
MID = 58.5
9.3

Instructions for Use –SCHMIDT®Flow Sensor SS 20.250 Seite 9
Accessories
The following accessories are available for mounting the SCHMIDT®Flow
Sensor SS 20.250.
Type / art. no.
Drawing
Assembly
Mounting flange
301048
- Immersion sensor
- Wall (planar surface)
- Attachement with:
3 screws (Ø < 5 mm)
- Material:
Aluminium anodized
Steel gal. (lock srew)
PTFE (clamping ring)
- Atmospheric pressure use
Wall mounting
flange
520181
- Immersion sensor
- Wall (planar surface)
- Attachement with:
2 screws M54
- Material:
Stainless steel 1.4404
PTFE (clamping ring)
Viton (O-Ring)
- Atmospheric pressure use
(pressure tight ≤500 mbar)
Compression
fitting
532160
G1/2
39
SW17
SW27
14 Ø9,2+0,1
- Immersion sensor
- Pipe (typ.); wall
- Screwing into a clamp
- Material:
Stainless steel 1.4571
PTFE (clamping ring)
- Atmospheric pressure use
Compression
fitting
517206
- Immersion sensor
- Pipe (typ.); wall
- Screwing into a clamp
- Material:
Brass
PTFE (clamping ring5)
NBR (O-Ring)
- Atmospheric pressure use
Clamp
a.) 524916
b.) 524882
- Internal thread Rp½
- Material:
a.) Steel, black
b.) Stainless steel 1.4571
Table 3
4
Countersunk head, not included in the delivery
5
Sealing ring splitted (in half)
55
20
38
18
5,8
9
51
12
1/2G
SW24
SW27
9
26,6
34
Rp 1/2

Instructions for Use –SCHMIDT®Flow Sensor SS 20.250 Seite 10
4 Electrical connection
The sensor is equipped with a 5-pin cable firmly fixed to the housing pipe
with open cable ends (pin assignment refers to Table 4).
Designation
Function
Wire color of cable
Power
Operating voltage: ±UBin DC mode
Operating voltage: U~ in AC mode
Brown
Analog wN
Output signal: Flow velocity
Yellow
Analog TM
Output signal: Temperature of medium
Green
GND
Operating voltage: ±UBin DC mode
Operating voltage: U~ in AC mode
White
AGND
Reference ground of analog outputs
Gray
Table 4
The cable has a standard length of 2 m; further lengths from 3 ... 100 m
can be ordered optionally.
Electrical assembly
During electrical installation ensure that no voltage is applied and
inadvertent activation is not possible.
The metallic housing of the sensor is indirectly coupled to GND (VDR, in
parallel with 100 nF) and should be connected to an anti-interference po-
tential, e.g. earth (depending on the shielding concept).
The appropriate protection class III (SELV) respective PELV (ac-
cording EN 50178) has to be considered.
Operating voltage
For proper operation the sensor requires DC or AC voltage with a nominal
value of 24 V(eff) with permitted tolerance of ±10 %. Typical operating cur-
rent is approx. 60 mA and at maximum 100 mA
6
.
Only operate sensor within the defined range of operating volt-
age (24 V DC / ACeff ± 10 %).
Undervoltage may result in malfunction; overvoltage may lead
to irreversible damages.
The specifications for the operating voltage are valid for the internal con-
nection of the sensor. Voltage drops generated due to cable resistances
must be considered by the customer.
6
Both signal outputs 22 mA (maximum measuring values), minimum operating voltage.
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