Schmidt SS 20.500 Bedienungsanleitung

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

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

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

, alcohols etc.

oHigh soiling tolerance

oHigh chemical media resistance

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.

Only compact sensor; remote version is limited to atmospheric applications.

Corresponds to the actual velocity under standard conditions.

Use of hydrogen peroxide only with uncoated version.

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

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.

Made of coloured polycarbonate

G1/2

40 18 16

SW32

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

, 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.

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

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.

Deviation < 1 % of the measured value

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

Length of whole measuring distance

Length of inlet distance

Length of outlet distance

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

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

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

and is given in Table 2.

For example, honeycombs made of plastic or ceramics; profile factor may change.

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:

 



 

󰇗

Pipe Ø

Measuring range of volumetric flow [m3/h]

Inner

Outer

For sensor measuring range

[mm]

1 m/s

2.5 m/s

10 m/s

20 m/s

35 m/s

0.710

70.3

76.1

198

347

0.710

76.1

82,5

116

233

407

0.720

82.5

88.9

139

277

485

0.740

100.8

108.0

213

425

744

0.750

107.1

114.3

243

486

851

0.760

125.0

133.0

336

672

1.175

0.775

131.7

139.7

380

760

1.330

0.795

150.0

159.0

126

506

1,012

1,770

0.810

159.3

168.3

145

581

1,162

2,034

0.820

182.5

193.7

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/

Inner diameter of pipe [m]

Cross-section area of pipe [m2]

Standard flow velocity in pipe centre [m/s]

Average standard flow velocity in tube [m/s]

Profile factor (for pipes with circular cross-sections)



Standard volumetric flow [m3/s]

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