Schmidt SS 20.500 User manual

SCHMIDT®Flow Sensor
SS 20.500
Instructions for Use

Instructions for Use –SCHMIDT®Flow Sensor SS 20.500 Page 2
SCHMIDT®Flow Sensor SS 20.500
Table of Contents
1Important information.......................................................................3
2Application range.............................................................................4
3Mounting instructions.......................................................................5
4Electrical connection......................................................................21
5Signalling.......................................................................................24
6Commissioning..............................................................................28
7Information concerning operation..................................................29
8Service information........................................................................31
9Technical data ...............................................................................34
10 Declaration of conformity...............................................................35
Imprint:
Copyright 2019 SCHMIDT Technology GmbH
All rights reserved
Version 523375.02F
Subject to modifications

Instructions for Use –SCHMIDT®Flow Sensor SS 20.500 Page 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
carefully, before putting the unit into operation.
Working on a pressurized system as well as assembly, electrical in-
stallation, commissioning and operation of the sensor may only be
carried out by trained specialists. Safety and accident prevention reg-
ulations must be observed.
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 (refer to
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
All the symbols used in this manual are explained in the following section.
Danger warnings and safety instructions - please read them!
Non-observance of these instructions maylead to personal injury
or malfunction of the device.
General note
All dimensions are indicated in mm.
!

Instructions for Use –SCHMIDT®Flow Sensor SS 20.500 Page 4
2 Application range
The SCHMIDT®Flow Sensor SS 20.500 (article number 521501) is de-
signed for stationary measurement of the flow velocity as well as the tem-
perature of air and gas at working pressure of up to 10 bar
1
.
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
2
wN, based on standard
conditions of 1013.25 hPa and 20 °C. Thus, the resulting output signal is
independent from the pressure and temperature of the measuring me-
dium.
The sensor has the following special features in connection with its unique
patented sensor tip design:
oOmnidirectional measurement recording
oHigh sensitivity (lower measuring threshold: 0.06 m/s)
oHigh turn down ratio (max. measuring range: 50 m/s)
oNo undercuts
oSterilizability using hydrogen peroxide
3
, alcohols etc.
oHigh soiling tolerance
oHigh chemical media resistance
4
These features predetermine that the sensor is used, for example in:
Clean room
Flow channel or duct
Free-space application
When using the sensor outdoors, it must be protected against
direct exposure to the weather.
Mechanical versions
The sensor SS 20.500 is available in a version as compact sensor (probe
is fixed at housing) and as a remote sensor (the probe is connected with
its sensor housing via a cable).
The remote version is limited to atmospheric applications.
1
Only compact sensor; remote version is limited to atmospheric applications.
2
Corresponds to the actual velocity under standard conditions.
3
Use of hydrogen peroxide only with uncoated version.
4
Especially with optional coatings.
!
!

Instructions for Use –SCHMIDT®Flow Sensor SS 20.500 Page 5
3 Mounting instructions
General information on handling
The flow sensor SS 20.500 is a precision instrument with high measuring
sensitivity, which can be achieved only by means of fine structure of the
measuring probe (see Figure 3-1). Therefore, avoid applying mechanical
force to the probe tip.
Figure 3-1
Especially when inserting or extracting the probe into/from through-chan-
nels (e.g. in a through-bolt joint) even slight tilting can lead to damage of
the tip.
Therefore, SCHMIDT Technology delivers the sensor with a protective
cap
5
placed onto the probe tip, which should be removed only during final
installation in longitudinal direction. Moreover, vice versa when dismount-
ing the sensor the protective cap must be attached in place immediately.
When handling the sensor generally proceed with great care.
The sensor probe can be damaged irreversibly due to mechani-
cal loads.
Leave the protective cap during mounting as long as possible
attached and handle the sensor with care.
5
Made of coloured polycarbonate
66
L
67
G1/2
9
9
40 18 16
SW32
45
45
!

Instructions for Use –SCHMIDT®Flow Sensor SS 20.500 Page 6
Systems with overpressure
The compact version of the SS 20.500 is designed for a maximum working
pressure of 10 bar. As long as the medium to be measured is operated
with overpressure, make sure that:
There is no overpressure in the system during mounting.
Mounting and dismounting of the sensor in pipes can be car-
ried out only as long as the system is in depressurized state.
Only suitable pressure-tight mounting accessories are used.
Appropriate safety devices are installed to avoid unintended discard-
ing of the sensor due to overpressure.
For measurements in media with overpressure, appropriate
safety measures must be taken to prevent unintended discard-
ing of the sensor.
The through-bolt joints available from SCHMIDT Technology for over-
pressure applications (see subchapter "Accessories") contain a pressure
protection kit designed especially for this purpose. In case of other acces-
sories or alternative mounting solutions the customer must ensure corre-
sponding safety measures.
The components of the pressure protection kit (bolt, chain and
bracket) have to be checked regularly for integrity.
Flow characteristics
Local turbulences of the medium can cause distortion of measurement
results. Therefore, appropriate installation conditions must be guaranteed
to ensure that the gas flow is supplied to the measuring probe in a lami-
nar
6
, i.e. quiet and low in turbulence, state. The corresponding measures
depend on the system properties (pipe, flow box, outdoor environment
etc.), they are described in the following subchapters for different mount-
ing variants.
Correct measurements require laminar flow with as low turbu-
lence as possible.
6
The term “laminar” means here an airflow low in turbulence (not according to its physical
definition saying that the Reynolds number is < 2300).
!
!
!
!

Instructions for Use –SCHMIDT®Flow Sensor SS 20.500 Page 7
The probe element of the SS 20.500 consists of two basic elements (see
Figure 3-2):
The heated measuring element in the probe tip (heater):
The barbell-shaped probe tip enables an omnidirectional flow meas-
urement vertically to the longitudinal axis of the probe. Furthermore,
the flow guiding disks allow deviation from the strictly vertical direction
of recording of up to 45° (see Figure 3-1) without significant impact
on the measurement result
7
.
The centre of the barbell-shaped element also referred to by specifi-
cation of probe length (L) is the actual measuring point of the flow
measurement and must be placed in the flow as advantageous as
possible, for example in the centre of the pipe (also see Figure 3-5).
Position the barbell-shaped segment always at the position
advantageous for the flow measurement.
The measuring sleeve for medium temperature recording (T-sleeve):
The sleeve must be positioned directly in the flow field (see Figure
3-2) to be able to detect changes of the medium temperature directly.
Figure 3-2
The minimum immersion depth (MID) of the probe required here is
58 mm. The sleeve must not contact the mounting fixture, the wall or
similar because this will cause interference to the flow and tempera-
ture measurement.
The temperature-measuring sleeve must be positioned di-
rectly in the main flow.
7
Deviation < 1 % of the measured value
!
T
min
!
MID
Heater
T-sleeve

Instructions for Use –SCHMIDT®Flow Sensor SS 20.500 Page 8
Mounting in pipes with circular cross-section
The mounting in a flow guiding pipe is carried out by means of a through-
bolt joint (for details refer to subchapter "Mounting with through-bolt joint").
The installation of the sensor must be performed at the point with laminar
(low turbulence) flow profile to guarantee correct measurement results.
The easiest method to achieve this is to provide a sufficiently long and
straight distance without disturbances (such as edges, seams, bends etc.)
in front (inlet) and behind the sensor (outlet; see installation drawing Fig-
ure 3-3). It is also necessary to pay attention to the design of the outlet
distance because disturbances also generate turbulences against flow di-
rection.
Figure 3-3
L
Length of whole measuring distance
L1
Length of inlet distance
L2
Length of outlet distance
D
Inner diameter of measuring section
The absolute length of the corresponding distance is defined by the inner
diameter of the pipe because the flow abatement depends directly on the
aspect ratio of the measuring distance to diameter. Therefore, the required
abatement distances are specified as a multiple of the pipe diameter D.
Furthermore, the degree of turbulence generated by the respective inter-
ference object plays a major role. A slightly curved bend directs the air
with relative low disturbance level compared to a valve generating mas-
sive turbulences with its abrupt change of the flow-guiding cross-section
requiring a relatively long distance for abatement.
The required abatement distances (in relation to the pipe inner diameter
D) for different disturbances are shown in Table 1.

Instructions for Use –SCHMIDT®Flow Sensor SS 20.500 Page 9
Flow obstacle up-
stream of measur-
ing section
Minimum
length of in-
let distance
(L1)
Minimum
length of out-
let distance
(L2)
Light bend (< 90°)
10 x D
5 x D
Reduction, expan-
sion, 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 1
This table lists the minimum values required in each case. If it is not pos-
sible to observe the specified abatement distances, increased deviations
of the measurement results are to be expected or it is necessary to take
additional measures, for example to use flow rectifiers
8
.
Under laminar conditions a quasi-parabolic speed profile is formed over
the pipe cross-section, whereas the flow velocity at the pipe walls remains
almost zero, in the middle of the pipe it reaches the optimum measuring
point, its maximum wN. This measurement value can be converted to an
average speed
N
w
constant over the pipe cross-section by means of a
correction factor, the so-called profile factor PF. The profile factor depends
on the pipe diameter
9
and is given in Table 2.
8
For example, honeycombs made of plastic or ceramics; profile factor may change.
9
Here interior air friction as well as obstruction caused by sensor is considered.

Instructions for Use –SCHMIDT®Flow Sensor SS 20.500 Page 10
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:
 

 
󰇗
PF
Pipe Ø
Measuring range of volumetric flow [m3/h]
Inner
Outer
For sensor measuring range
[mm]
[mm]
1 m/s
2.5 m/s
10 m/s
20 m/s
35 m/s
0.710
70.3
76.1
10
25
99
198
347
0.710
76.1
82,5
12
29
116
233
407
0.720
82.5
88.9
14
35
139
277
485
0.740
100.8
108.0
21
53
213
425
744
0.750
107.1
114.3
24
61
243
486
851
0.760
125.0
133.0
34
84
336
672
1.175
0.775
131.7
139.7
38
95
380
760
1.330
0.795
150.0
159.0
51
126
506
1,012
1,770
0.810
159.3
168.3
58
145
581
1,162
2,034
0.820
182.5
193.7
77
193
772
1,544
2,703
0.840
206.5
219.1
101
253
1,013
2,026
3,545
0.840
260.4
273.0
161
403
1,610
3,221
5,637
0.845
309.7
323.9
229
573
2,292
4,583
8,020
0.845
339.6
355.6
276
689
2,755
5,511
9,644
0.850
388.8
406.4
363
908
3,633
7,266
12,715
0.850
437.0
457.0
459
1,147
4,590
9,179
16,064
0.850
486.0
508.0
568
1,419
5,677
11,353
19,868
0.850
534.0
559.0
685
1,713
6,853
13,706
23,986
0.850
585.0
610.0
822
2,056
8,225
16,450
28,787
0.850
631.6
660.0
959
2,397
9,587
19,175
33,555
Table 2
SCHMIDT Technology provides a "flow calculator" on its homepage
(page: "Service & Support") for calculation of flow velocity or volume flow
in pipes for various sensor types:
http://www.schmidt-sensors.com/ or http://www.schmidttechnology.com/
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/s]