Schmidt SS 20.651 User manual

SCHMIDT®Flow Sensor
SS 20.651
Instructions for Use

Instructions for Use SS 20.651 page 2
SCHMIDT®Flow Sensor
SS 20.651
Table of contents
1Important information.......................................................................3
2Application range.............................................................................3
3Mounting..........................................................................................4
4Electrical connection........................................................................7
5Commissioning..............................................................................15
6Service information........................................................................16
7Dimensions....................................................................................20
8Technical table ..............................................................................21
9Declaration of conformity...............................................................23
Imprint:
Copyright 2016 SCHMIDT Technology GmbH
All rights reserved
Version: 547608.02B
Subject to modifications

Instructions for Use SS 20.651 page 3
1 Important information
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 or non-compliance with these instructions will
become void.
Tampering with the device in any way whatsoever - with the excep-
tion of the designated use and the operations described in these in-
structions for use - will forfeit any warranty and exclude any liability.
The device 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 or machinery.
SCHMIDT Technology cannot give any warranty as to its suitability
for a certain purpose and cannot be held liable for errors contained in
these instructions for use or for accidental or sequential damage in
connection with the delivery, performance or use of this device.
The following symbol has to be observed:
Danger warnings and safety instructions. Read carefully!
Non-observance of these instructions may lead to injury of
personal or malfunction of the device.
2 Application range
The SCHMIDT®flow sensor SS 20.651 is designed for stationary
measurement of the flow velocity as well as the temperature of air. The
sensor measures standard velocity
1
wN(unit: m/s) based on standard
conditions of 1013.25 hPa and 20 °C. The output signal is linear and in-
dependent of pressure and temperature of the measured medium.
The basic version (without coating) is suitable only for clean air. Espe-
cially the occurrence with aggressive components (e.g. sulfur, fluor, na-
trium, chlorine, phosphor, etc.) can be done only on the customer's own
responsibility. With optional coating (Parylene) the sensor exhibits a
higher tolerance concerning pollution and an increased media re-
sistance. The respective suitability has to be considered in each case
due to the different environmental conditions.
When using the sensor outdoors, it must be protected against
direct exposure to the weather.
1
Corresponds to actual velocity under standard conditions
!
!

Instructions for Use SS 20.651 page 4
3 Mounting
Determination of the place of installation
Correct measurements require a flow low in turbulence. This can be
achieved by providing sufficiently long and straight distances without dis-
turbances in front of and behind the sensor.
The minimum inlet and outlet distances depend on the degree of dis-
turbance of the flow obstacle upstream of the measuring distance and
the inner pipe diameter
2
D (see Figure 1 and Table 1).
Figure 1
Flow obstacle
upstream of sen-
sor position
Minimum
length inlet
(L1)
Minimum
length outlet
(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
(3-dimensional
change in direction)
35 x D
5 x D
Shut-off valve
45 x D
5 x D
Table 1 Minimum measuring distances depending on the flow obstacles
2
Minimum inner pipe diameter: 25 mm

Instructions for Use SS 20.651 page 5
Mounting method
The SS 20.651 is mounted by means of a through-bolt joint (included by
delivery) which clamps the sensor probe frictionally. Due to the different
operating conditions (temperature and pressure range), there are differ-
ent types (see Table 2):
Max. temperature
Max. pressure
fitting
seal
spare part no.
200 / 350 °C
atmospheric
brass
no
549311
200 °C
16 bar
1.4571
FKM
535092
350 °C
16 bar
1.4571
clamping ring
549312
Table 2 Types of compression fittings
Systems with overpressure
The SS 20.615 is designed for atmospheric conditions (standard), op-
tionally for a working pressure up to 16 bar. As long as the medium is
operated with overpressure, make sure that:
There is no overpressure in the system during mounting.
Mounting and dismounting of the sensor can be carried out
only as long as the system is in a 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 dis-
carding of the sensor.
If other accessories than the delivered pressure protection kit or alterna-
tive mounting solutions are used, the customer must ensure the corre-
sponding safety measures.
Pressure-tight mounting, fastening of the screw pipe connec-
tion and discarding protection must be checked before pres-
sure is applied. These tightness checks must be repeated at
reasonable intervals.
All components of the pressure protection kit (bolt, chain and
bracket) have to be checked regularly for integrity.
!
!
!
!

Instructions for Use SS 20.651 page 6
Thermal boundary conditions
With medium temperatures exceeding the permitted ambient tempera-
ture of the electronic components, a free cooling section of the probe of
at least 50 mm must be provided (see Figure 2) to prevent the electronic
components located in the electronic housing from being influenced by
the temperature.
Figure 2
Make sure that the transmission of the medium temperature
does not cause the temperature to exceed the permitted oper-
ating temperature of the electronics.
On the housing side, the sensor tube should project out of the
measuring tube in the air (without insulation) at a length of at
least 50 mm (if ambient air is cold enough to cool it down).
Alignment of the sensor
The sensor head must be placed in the middle of the pipe (see Figure 1)
and adjusted correctly relative to the flow direction. A sensor mounted in
the wrong direction rotated by 180° leads to wrong (too high) measuring
values. As installation aid, a flow arrow is located on the enclosure cov-
er. It must corresponds to the flow direction.
The tilting of the measurement direction relative to the flow must not ex-
ceed ± 3°, otherwise it can lead to major measurement deviations
3
.
The sensor measures unidirectionally and must be adjusted
correctly relative to the flow direction.
The axial tilting of the sensor head relative to the flow direc-
tion should not exceed 3°.
General note:
Do not use the aligning surface of the housing for mechanical
alignment, such as locking. There is a risk of damage to the
sensor.
3
Deviations > 1% of the measured value
!
!
!

Instructions for Use SS 20.651 page 7
4 Electrical connection
Make sure that no operating voltage is active during electrical
installation and that the operating voltage cannot be switched
on inadvertently.
Specification of the plug-in connector (firmly integrated in the housing):
Number of connection pins: 8 (plus shield connection at the metallic housing)
Type: male
Fixation of connecting cable: M12 thread (spigot nut at the cable)
Type of protection: IP67 (with screwed cable)
Model: Binder, series 763
Pin numbering: View of plug-in connector of the sensor
Figure 3
Pin assignment of the connector can be seen in the following Table 3.
Pin
Designation
Function
Wire color
1
Pulse 1
Output signal flow / volume (digital: impulse)
White
2
UB
Operating voltage: 24 VDC ± 20%
Brown
3
Analog TM
Output signal temperature of medium (analog: U / I)
Green
4
Analog wN
Output signal flow (analog: U / I)
Yellow
5
AGND
Reference potential for analog outputs
Gray
6
Pulse 2
Output signal flow / volume (digital: relay)
Pink
7
GND
Operating voltage: Ground
Blue
8
Pulse 2
Output signal flow / volume (digital: relay)
Red
Shield
Electromechanical shielding
Meshwork
Table 3
The analog signals have an own AGND reference potential which is di-
rectly connected to GND of the operating voltage within the sensor.
The specified wire colors are valid using a connecting cable delivered by
SCHMIDT®.
The appropriate protection class III (SELV) respective PELV
(EN 50178) has to be considered.
!
!

Instructions for Use SS 20.651 page 8
Operating voltage
For proper operation, the sensor requires DC voltage with a nominal val-
ue of 24 VDC with a permitted tolerance of ± 20 %.
Deviating values can lead to measurement errors or even defects and,
therefore, should be avoided.
Only operate the sensor in the defined range of operating volt-
age (24 VDC ± 20 %).
Undervoltage may result in malfunction, overvoltage may lead
to irreversible damage.
The operating current of the sensor (including analog signal currents) is
normally approx. 50 mA (max. 250 mA).
The specifications for the operating voltage are valid for the connection
to the sensor. Voltage drops generated due to line resistances must be
taken into account by the customer.
Wiring of analog outputs
Both analog outputs, for flow and temperature, are designed as high-side
drivers with "Auto-U/I" characteristic which are short circuit protected
against both rails of the operating voltage.
The loading resistance RLmust be connected between the correspond-
ing signal output and the electronic reference potential AGND or GND of
the sensor.
Depending on the resistance value RL, the signal electronics switches
automatically between its operation as voltage interface (mode: U) or
current interface (mode: I), hence the designation "Auto-U/I". The switch-
ing threshold is in range between 500 and 550 (for details, refer to the
next subchapter Signaling of analog outputs).
However, a low load resistance value in voltage mode may cause signifi-
cant voltage losses via line resistances RW,S, which can lead to measur-
ing errors.
For the voltage mode, a measuring resistance of at least
10 kis recommended.
The maximum load capacity CLis 10 nF.
!
!

Instructions for Use SS 20.651 page 9
The following points must be also taken into account:
Use of only one analog output
It is recommended to terminate both analog outputs with the same
resistance value, even if only one of the two analog outputs is used.
Unused analog outputs
In this case, both outputs can remain disconnected or should be
terminated with high impedance against A/GND (with the same re-
sistance value).
Short circuit mode
In case of a short circuit against the positive rail of the operating
voltage (+UB), the signal output is switched off.
In case of a short circuit against the negative rail (A/GND) of the op-
erating voltage, the output switches to current mode (RLis calculated
to 0 ) and provides the required signal current.
If the signal output is connected to +UBvia a resistance, the value RL
is calculated incorrectly and false signal values are caused.
Signaling of analog outputs
Switching characteristic “Auto-U/I”
Range of resistance value RL
Signaling mode
Signaling range
≤ 500 (550) 
Current (I)
4 ... 20 mA
> 500 (550) 
Voltage (U)
0 ... 10 V
Table 4 Switching characteristic “Auto-U/I”
A hysteresis of approx. 50 ensures a stable transition behavior
which is shown in Figure 4 below.
Figure 4
Depending on the set output signal, accuracy of the switching point
detection can be reduced. Therefore, it is recommended to select the
R [ ]
L
0500 550
Modus
I
U
Mode

Instructions for Use SS 20.651 page 10
load resistance RLin such a way that a secure detection can be
maintained (< 300 for current mode and > 1 kfor voltage mode).
For measuring of RLin an actual zero signal (voltage mode), the
electronics generates test pulses that correspond to an effective val-
ue of approx. 1 mV. However, the latest measuring devices may trig-
ger in response to such a pulse in the DC voltage measuring mode
and display short-term measuring values of up to 20 mV. In this
case, it is recommended to install an RC filter before the measuring
input with a time constant of 20 … 100 ms.
Severe interferences on the connection cable may shift the switching
threshold outside specification. In this case the use of isolated ampli-
fiers for the measuring signals is recommended.
Error signaling
In current mode, the interface outputs 2 mA
4
.
In voltage mode, the output switches to 0 V.
Representation of measuring range
The measuring range of the corresponding measuring value is
mapped in a linear way to the signaling range of its associated ana-
log output, depending on signal type.
For flow velocity measurement, it ranges from zero flow to the end of
the measuring range wN,max (see Table 5).
Voltage mode (U)
Current mode (I)
wNOut
N
NU
V
w
w,
max,
10 
)4(
16 ,
max, mAI
mA
w
wwNOut
N
N
Table 5 Representation specification for flow measurement
The measuring range of the medium temperature TMstarts at 0 °C
and reaches up to TM,max = 200 / 350 °C (see Table 6).
4
In accordance with the Namur specification
110 wN [%]
020 40 8060 100
IOut
[mA]
20
4
21,6
12
8
16
U
Out
[V]
0
110
w
N
[%]
10
0
20
11
40
80
60
100
4
2
6
8