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:

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.

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

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).

Corresponds to the actual velocity under standard conditions.

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

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).

Length of entire measuring distance

Length of run-in distance

Length of run-out distance

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

Alternatively flow rectifiers, e.g. honeycomb ceramics, can be used.

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

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





AwV

wPFw





Tube Ø

Measuring range of volumetric flow [m3/h]

Inside

Outside

for sensor measuring range

[mm]

1 m/s

2.5 m/s

10 m/s

20 m/s

0.710

70.3

76.1

198

0.720

82.5

88.9

139

277

0.740

100.8

108.0

213

425

0.760

125.0

133.0

336

672

0.795

150.0

159.0

126

506

1,012

0.820

182.5

193.7

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:

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/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:

RNN

hb hb

PFV

AwV

wPFw

hb hb

































































bK / hK

Width / height of square chamber [m]

Inner diameter of equivalent pipe [m]

Cross-section area of equivalent pipe [m2]

Flow velocity in the middle of duct / pipe [m/s]

Average flow velocity in equivalent pipe [m/s]

Profile factor of pipe3with inner diameter DR



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.

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

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

Sensor length [mm]

Outer diameter of the pipe [mm]

Length of the weld-in sleeve [mm]

Sensor tube setting length [mm]

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

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

Countersunk head, not included in the delivery

Sealing ring splitted (in half)

5,8

1/2G

SW24

SW27

26,6

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

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.

Both signal outputs 22 mA (maximum measuring values), minimum operating voltage.

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