DNS/VNS
Pressure switches and vacuum switches with stainless steel
sensors (1.4571)
Pressure switches of the DNS series are suitable
for monitoring and controlling pressures in
chemical plants, process engineering and
any situation where the pressure of aggressive
liquids and gases must be monitored.
SIL 2 according IEC 61508-2
DNS3-201
Technical data
Pressure connection
External thread G 1/2 (pressure gauge
connection) according to DIN 16 288 and
internal thread G 1/4 according to
ISO 228 Part 1.
Switching device
Robust housing (200) made of seawater-
resistant diecast aluminium GD Al Si 12.
Protection class
IP 54, in vertical position.
Pressure sensor materials
Pressure bellows and all parts in contact with
medium. X 6 Cr Ni Mo Ti 17122 Material no.
1.4571
Mounting position
Vertically upright and horizontal.
Max. ambient temperature at switching
device
–25…+70 °C.
Max. medium temperature
The maximum medium temperature at the
pressure sensor must not exceed the permitted
ambient temperature at the switching device.
Temperatures may reach 85°C for short
periods.
Higher medium temperatures are possible
provided the above limit values for the
switching device are ensured by suitable
measures (e.g. siphon).
Mounting
Directly on the pressure line (pressure
gaugeconnection) or on a flat surface with two
4 mm Ø screws.
Switching pressure
Adjustable from outside with screwdriver.
Switching differential
For values see Product Summary.
Contact arrangement
Single-pole changeover switch.
Switching
capacity
Normal
250 VAC 250 VDC 24 VDC
(ohm) (ind) (ohm) (ohm)
8A 5A
0.3 A
8A
Product Summary
Type
Setting range
Switching
differential
(mean values)
Max.
permissible
pressure
Dimen-
sioned
drawing
page 25 + 26
3
6
6
6
6
16
16
16
25
bar
bar
bar
bar
bar
bar
bar
bar
bar
1 + 18
1 + 16
1 + 18
1 + 16
* At very high vacuums, close to the theoretical maximum of –1 bar, the switch may not be usable in
view of the special conditions of vacuum engineering. However, the pressure switch itself will not be
damaged at maximum vacuum.
Plastic coating
The diecast aluminium housing in GD Al Si is
chromated and stove-enamelled with resistant
plastic. Corrosion tests with 3% saline solution
and 30 temperature changes from +10 to
+80°C showed no surface changes after 20
days.
-DNS/VNS
see page 66
s
Protection Class:
IP 54
Accessories
Solenoid valves
Calibration
The
DNS
and
VNS
series are calibrated for falling pressure. This means that the adjustable switching
pressure on the scale corresponds to the switching point at falling pressure. The reset point is higher
by the amount of the switching differential. (See also page 27, 1. Calibration at lower switching point).
Flow monitors
Switching differential adjustable
VNS301–203
–250…+100 mbar
VNS111–203
–1*…+0.1
bar
DNS025–203
0.04…0.25
bar
DNS06–203
0.1…0.6
bar
DNS1–203
0.2…1.6
bar
DNS3–203
0.2…2.5
bar
DNS6–203
0.5…6
bar
DNS10–203
1…10
bar
DNS16–203
3…16
bar
70 –300
90 –550
60 –300
80 –400
100 –600
0.15– 1.5
0.25– 2.0
0.45– 2.5
0.8– 3.5
mbar
mbar
mbar
mbar
mbar
bar
bar
bar
bar
3
6
6
6
6
16
16
16
25
bar
bar
bar
bar
bar
bar
bar
bar
bar
1 + 15
Temperature sensors
Switching differential not adjustable
VNS301-201
-250…+100 mbar
45 mbar
VNS111-201
-1*…+0.1
bar
50 mbar
DNS025-201
0.04…0.25
bar
30 mbar
DNS06-201
0.1…0.6
bar
40 mbar
DNS1-201
0.2…1.6
bar
60 mbar
DNS3-201
0.2…2.5
bar
0.1 bar
DNS6-201
0.5…6
bar
0.15 bar
DNS10-201
1…10
bar
0.3 bar
DNS16-201
3…16
bar
0.5 bar
1 + 15
Thermostats
Pressure transmitters
All components of the sensor system
are made of high-quality stainless steel (1.4571)
and welded using the latest methods without
filler metals. The pressure sensor
is gasket-free plasma-welded.
Pressure switches
Mechanical pressure switches
Liquids and gases
41
42
Mechanical pressure switches
Liquids and gases
DNS/VNS
Pressure and vacuum switches with stainless steel sensors
(1.4571)
Chemical version (switching housing with
surface protection)
Pressure switches of the DNS series are
suitable for monitoring and controlling pressures
in chemical plants, process engineering and any
situation where the pressure of aggressive
SIL 2 according IEC 61508-2
liquids and gases must be monitored. All
components of the sensor system are made
from high-quality stainless steel (1.4571) and
welded using the latest methods without filler
metals. The pressure sensor is gasket free
plasma welded.
DNS6-351
Technical data
Pressure connection
External thread G 1/2"
(pressure gauge
connection) according
to DIN 16 288 and
internal thread G 1/4"
according to ISO 228
Part 1
Switching device
Robust housing (300)
made of seawater-
resistant diecast
aluminium GD Al Si 12
Protection class
IP 65, in vertical position
Pressure sensor
Pressure bellows and
materials
all parts in contact
with medium
X 6 Cr Ni Mo Ti 17122
Material no. 1.4571
Mounting position
Vertically upright and
horizontal
Max. ambient
temperature
at switching device
–25 to +70 °C
Max. medium
The maximum medium
temperature
temperature at the
pressure sensor must
not exceed the permitted
ambient temperature
at the switching device.
Temperatures may reach
85 °C for short periods.
Higher medium
temperatures are
possible provided
the upper limit at
the switching device
is ensured by suitable
measures (e.g. siphon).
Plastic coating
The diecast aluminium
housing in GD Al Si
is chromated and
stove-enamelled with
resistant plastic.
Corrosion tests with 3%
saline solution and 30
temperature changes
from +10 to +80°C
showed no surface
changes after 20 days
Contact arrangement
Single-pole changeover
switch
Switching
capacity
Normal
250 VAC 250 VDC 24 VDC
(ohm) (ind) (ohm) (ohm)
8A 5A
0.3 A
8A
Type
Setting range
Switching
differential
(mean value)
Max.
permissible
pressure
Dimen-
sioned
drawing
page 25 + 26
Hysteresis not adjustable
VNS301-351
-250…+100 mbar
VNS111-351
-1*…+0,1
bar
DNS025-351
0,04…0,25
bar
DNS06-351
0,1…0,6
bar
DNS1-351
0,2…1,6
bar
DNS3-351
0,2…2,5
bar
DNS6-351
0,5…6
bar
DNS10-351
1…10
bar
DNS16-351
3…16
bar
45
50
30
40
60
0,1
0,15
0,3
0,5
mbar
mbar
mbar
mbar
mbar
bar
bar
bar
bar
3
6
6
6
6
16
16
16
25
bar
bar
bar
bar
bar
bar
bar
bar
bar
2 + 15
2 + 18
2 + 16
* At very high vacuums, close to the theoretical maximum of –1 bar, the switch may not be usable in
view of the special conditions of vacuum engineering. However, the pressure switch itself will not be
damaged at maximum vacuum.
Calibration
The
DNS
and
VNS
series are calibrated for falling pressure. This means that the adjustable switching
pressure on the scale corresponds to the switching point at falling pressure. The reset point is higher by
the amount of the switching differential. (See also page 27, 1. Calibration at lower switching point).
DNS/VNS
see page 66
s
Protection Class:
IP 65
Mechanical pressure switches
Technical features / Advantages
Diecast aluminium housing
IP 54 or IP 65
version also available
Wall mounting
or directly on the pressure line
Switching element (microswitch)
Lead sealable setpoint adjustment
Setting spindle locking element
Stainless steel sensor housing
Stainless steel bellows
with internal stop
Pressure connection
G 1/2" external
G 1/4" internal
Centring pin
Accessories
Solenoid valves
Flow monitors
Terminal connection
or plug connection to
DIN EN175301 Form A
Temperature sensors
Thermostats
Pressure transmitters
Pressure switches
Mechanical pressure switches
Technical features/Advantages
19
20
Mechanical pressure switches
Definitions
Definitions
Pressure data
Overpressure
Pressure
over
the relevant atmospheric pressure. The reference point is
atmospheric pressure.
Pressure
under
the relevant atmospheric pressure. The reference point is
atmospheric pressure.
Overpressure relative to absolute vacuum.
Vacuum
Absolute pressure
Differential pressure
Difference in pressure between 2 pressure measuring points.
Relative pressure
Overpressure or vacuum relative to atmospheric pressure.
Pressure data in all FEMA documents refers to relative pressure.
That is to say, it concerns pressure differentials relative to atmospheric pressure.
Overpressures have a positive sign, vacuums a negative sign.
Permissible working pressure
(maximum permissible pressure)
The maximum working pressure is defined as the upper limit at which the operation, switching reliability
and water tightness are in no way impaired (for values see Product summary).
Bursting pressure (test pressure)
Type-tested products undergo a pressure test certified by TÜV affirming that the bursting pressure
reaches at least the values mentioned in the Product summary. During the pressure tests the measuring
bellows are permanently deformed, but the pressurized parts do not leak or burst. The bursting pressure
is usually a multiple of the permissible working pressure.
Setting range
Pressure range in which the cutoff pressure can be set with the setting spindle.
Pressure units
Unit
bar
mbar
Pa
kPa
MPa
(psi) Ib/m
2
1
1
1
1
1
bar
mbar
Pa
kPa
MPa
1
0.001
10
-5
0,01
10
1000
1
0.01
10
10
4
10
5
100
1
1000
10
6
100
0.1
0.001
1
1000
0.1
10
-4
10
-6
0.001
1
14.5
0.0145
1.45 · 10
-4
0,145
145
In FEMA documents pressures are stated in
bar
or
mbar.
Pressure data for a pressure
switchbased on the example
of DWR625:
Setting range: 0.5-6 bar
Perm. working pressure: 20 bar
Bursting pressure: >100 bar
Important:
All pressure data refers to overpressures or vacuums relative to atmospheric pressure.
Overpressures have a positive sign, vacuums a negative sign.
Definitions
Maximum pressure monitoring
RSP = SP – xd
Switching differential
Pressure transmitters
Accessories
Solenoid valves
Flow monitors
Temperature sensors
Thermostats
The switching differential (hysteresis) is the difference in pressure between the
switching point (SP)
and the
reset point (RSP)
of a pressure switch. Switching differential tolerances occur due to
tolerances in the microswitches, springs and pressure bellows. Therefore the data in the product
summaries always refers to average values. In the case of limiter functions the switching differential
has no significance, as one is only interested in the switching point at which cutoff occurs, not the
reset point. For a
controller function,
i. e. in the case of pressure switches used to switch a burner,
pump etc.
on and off,
a pressure switch with an
adjustable switching differential
should be
chosen. The switching frequency of the burner or pump can be varied by changing the switching
differential.
Adjustable switching differential/ calibration
In the case of pressure switches with adjustable switching differential, the hysteresis can be set within
the specified limits. The switching point (SP)
and
reset point (RSP) are precisely definable. When
setting the pressure switch, the switching differential situation and the type of factory calibration must
be taken into account. Some pressure switches (e.g. minimum pressure monitors of the DCM series)
are calibrated under "falling" pressure, i.e. switching under falling pressure takes place at the scale
value with the switching differential being above it. The device switches back at scale value +
switching differential. If the pressure switch is calibrated under rising pressure, switching takes place
at the scale value and the device switches back at scale value - switching differential (see direction of
action). The calibration method is indicated in the data sheets.
Minimum pressure monitoring
RSP = SP + xd
Direction of action
In principle, any pressure switch can be used for both maximum pressure and minimum pressure
monitoring. This excludes pressure limiters, whose direction of action (maximum or minimum) is
predefined. The only thing to remember is that the scale reading may deviate by the amount of the
switching differential. See example at bottom left: The scale value is 2.8 bar.
Maximum pressure monitoring
With rising pressure,
switching takes place once the preset switching pressure is reached (SP).
The reset point (RSP) is lower by the amount of the switching differential.
Minimum pressure monitoring
With falling pressure,
switching takes place once the preset switching pressure is reached (SP).
The reset point (RSP) is higher by the amount of the switching differential.
Direction of action in vacuum range
It is particularly important to define the direction of action in the vacuum range.
Rising does not mean a rising vacuum, but rising pressure (as viewed from absolute "0"). "Falling"
pressure means a rising vacuum.
For example: Vacuum switch set to -0.6 bar falling means: Switching (SP) takes place under falling
pressure (rising vacuum) at -0.6 bar. The reset point is higher by the amount of the switching
differential (e.g. at -0.55 bar).
Setting a pressure switch
To define the switching point of a pressure switch exactly, it is necessary to determine the direction of
action in addition to the pressure. "Rising" means that switching takes place at the set value when the
pressure rises.
The reset point is then lower by the amount of the switching differential. "Falling" means exactly the
opposite.
Please note when specifying the setting of a pressure switch:
In addition to the switching point it is also necessary to specify the direction of action (falling or rising).
Example for selection of a pressure switch:
A pump is to be turned on at 2.8 bar and off again at 4.2 bar.
Chosen type: DCMV6 according to data sheet DCM. Setting: Scale pointer to 2.8 bar (lower switching
point). Switching differential to 1.4 bar (set according to pressure gauge).
Cutoff point: 2.8 bar +1.4 bar = 4.2 bar.
Pressure switches
Mechanical pressure switches
Definitions
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