VEGA Z728 User Manual

Zener barriers - operating instructions

Operating principle

1 Zener barriers - operating instructions

Application

• Zener barriers are used in control and instrumentation
systems for the processing of standardised signals, such as
20 mA and 10 V. Zener barriers contain intrinsically safe
circuits that are used to drive intrinsically safe field devices
within hazardous areas. The manufacturers data sheets
must be consulted.

• The relevant regulations and directives governing the
intended application must be observed.

Installation, commissioning

• Zener barriers are constructed to a protection classification
of IP20 and accordingly must be appropriately protected
from adverse conditions such as splashing water and soiling
in excess of pollution severity 2.

• Zener barriers must be installed outside the hazardous area!
Only those circuits identified as intrinsically safe may be
located within the hazardous area.

• When intrinsically safe field devices are interconnected with
the intrinsically safe circuits of the related Zener barriers, the
respective highest values (safety parameters) for the field
devices and the Zener barriers - in the sense of explosion
protection - must be observed (demonstration of intrinsic
safety). The EU certificate of conformity or EU prototype test
certificate must be followed. Particular importance is
attached to maintaining the "Special conditions" contained
in these certificates.

• When intrinsically safe circuits are employed in an explosive
dust atmosphere (zones 20 and 21), only appropriately
certificated field devices are permitted to be incorporated.

Installation and commissioning within zone 2

• The devices must be installed in switch boxes or distributor
boxes to protection category IP54 or better.

• The devices may be installed within zone 2. Only those
circuits identified as intrinsically safe are permitted to be
installed in zone 1 or zone 0 and in accordance with their
ignition protection category approval. The actual installation
of the intrinsically safe circuits is to be carried out in
accordance with the applicable installation regulations.

• When interconnecting intrinsically safe field devices with the
intrinsically safe circuits of the associated Zener barriers,
the respective highest values (safety parameters) of the field
device and the associated device, in the sense of explosion
protection, must be taken into account (demonstration of
intrinsic safety). The conditions stated on the EU certificates
of conformity or EU prototype test certificates must be
observed.

• In addition, for operation within zone 2, the statements of
conformity of the certifying authorities/declarations of
conformity of the manufacturer must be observed. Particular
importance is attached to maintaining the "Special
conditions" contained in these certificates.

• When intrinsically safe circuits are employed in an explosive
dust atmosphere (zones 20 and 21), only appropriately
certificated field devices are permitted to be incorporated.

Servicing and maintenance

The transmission characteristics of the devices remain stable
over long periods, so that regular adjustments or other
precautions are not required. This also means that no
maintenance work is required.

Fault elimination

No modifications may be made to devices that are operated in
connection with hazardous areas. Repairs must only be carried
out by specially trained and authorised personnel.

1.1 Operating principle

The Zener diodes in the barriers are connected in the reverse
direction. The breakdown voltage of the diodes is not
exceeded in normal operation.

Hazardous area Safe area

Resistor

R1

Zener diodes

Figure 1.1 Circuit diagram

ZD1

ZD2 ZD3

If this voltage is exceeded, due to a fault in the non-Ex-area,
the diodes start to conduct, causing the fuse to blow, thus
preventing the transfer of unacceptably high energy into the
hazardous area.

Terminals 7 and 8 are connected to the devices in the non­hazardous area. The single condition that these devices must
satisfy, is that they must not contain a source whose potential
relative to earth is greater than 250 V/253 V

253 V DC.

Fuse

F1

AC or 250/

eff

Terminals 1 and 2 are connected to the intrinsically safe
circuits in the hazardous area. If they are used in the
hazardous area, active intrinsically safe apparatus must be
certificated unless the electrical values of such apparatus do
not exceed any of the following values: 1.5 V; 0.1 A; 25 mW.

Pepperl+Fuchs Zener barriers are identified in terms of
voltage, resistance and polarity, e. g. 10 V, 50 Ohm, positive
polarity. These figures correspond to the Zener voltage U

and

z

the total resistance of all barrier components. They therefore
represent the safety values. The values stated on the type
identification label correspond to the "worst case" data for
U

) and Ik(Io) determined during certification.

z(Uo

I

is obtained by dividing Uz by the resistance R1. It should be

k

noted once again, however, that these values do not
correspond to the operating range of the Zener barrier.

Ideally, Zener diodes would not allow any current in the reverse
direction until the Zener voltage has been attained. In practice,
Zener diodes do allow a small leakage current, the value of
which increases as the applied voltage is increased.

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

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Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

Zener barriers - operating instructions

Operating principle

The operating range of a Zener barrier must therefore be such
that it is below the Zener voltage, so that the leakage current is
restricted to a minimum. Zener barriers are normally tested to
ensure that at the prescribed voltage the leakage current is
smaller than 10 µA.

Hazardous area Safe area

50 mA

Load

Figure 1.2 This figure shows a selection of leakage currents through

the Zener barriers under normal circumstances. The
Zener barriers conduct a maximum of 10 (1) µA leakage
current so long as the supply voltage is less than 25.5 V.
This is normal and has very little effect on the load. If the
voltage exceeds 25.5 V, the Zener diodes start to
conduct more current. This can have an effect on the
operating current and the accuracy. It is therefore
recommended that a controlled voltage source be used,
which maintains the voltage under the value at which the
diodes will start to conduct.
(A 24 V, 300 Ohm barrier is represented here as an
example)

10 µA

24 V

Power
supply

(+)

25.5 V

≤

(-)

These voltages are stated in the data sheet for a given barrier,
together with the leakage current. If the leakage current for a
given voltage differs from 10 µA, this is specifically stated.

Hazardous area Safe area

50 mA

Load

Figure 1.3 This figure shows that if the maximum permissible input

(supply) voltage is exceeded, the total current drains
through the Zener diodes, without reaching the explosive
surroundings.

24 V

Power
supply

(+)

25.5 V

>

(-)

Pepperl+Fuchs Zener barriers have a low series resistance,
given by the sum of the resistance R1 and the resistance value
of the fuse F1. Due to the low series resistance, an inadvertent
short-circuiting of terminals 1 and 2 can cause the fuse to blow.
In order to avoid this, some barriers are available with
electronic current limitation (CL-version).

If the Zener barriers are provided with a resistance, this limits
the short-circuit current to a safe value in the event of a short­circuit of the connecting wiring in the hazardous area or a
connection to earth of the wiring attached to terminal 1, as the
fuse blows.

Many barriers are available with a resistance connected
between the output terminals. These are used in
4 mA … 20 mA transmitter circuits. The resistance converts
the current in the intrinsically safe circuit into a voltage that can
be measured in the safe area.

Pepperl+Fuchs Zener barriers can be used in many
applications. In the simplest case, a single channel barrier with
a ground connection is used. But in many applications it is not
desirable that the intrinsically safe circuit is connected directly
to ground. If the circuit in the safe area is grounded, under
some circumstances grounding of the intrinsically safe circuit
can lead to faults within the system. In this case, quasi ground­free intrinsically safe circuits can be constructed with two or
more barriers. This floating circuitry can be simply achieved
with 2- or 3-channel barriers.

Double grounding of intrinsically safe circuits is not permitted.
The insulation voltage of the wiring and field devices,
measured with respect to ground, must be greater than
500 V AC. The permissible ambient temperature of the Zener
barriers is between -20 °C … 60 °C.

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

2

Zener barriers - operating instructions

y

Multi-channel barriers

1.2 Multi-channel barriers

Analogue circuits are often connected to two-channel barriers
(see Figure 1.5). Since there is no grounding on this type of
circuit, the system is a quasi floating one. It is termed "quasi
floating", because it is "one Zener voltage" above the ground
potential. Although it does not actually float, the signal-to-noise
ratio is improved.

A further advantage of multi-channel Zener barriers is that a
higher packing density can be achieved.

.

Hazardous area

4 mA ... 20mA

transmitter

Safe area

(+)

24 V

R

M

Power supply can
not be grounded.

Figure 1.4 Single-channel Zener barrier

1.3 Grounding of Zener barriers

Intrinsically safe circuits with Zener barriers without galvanic
isolation must be grounded. The cross-section of the ground

connection, using a copper conductor, must be at least 4 mm
(for further details see EN 60079-14, section 12.2.4). The
maintenance of these requirements prevents the occurrence of
a dangerous potential with respect to ground.

A fault of the type illustrated in figure 8.6 can cause a
dangerous spark if the Zener barrier is not grounded, but
grounding is provided via the field device in the intrinsically
safe circuit (Figure 1.5). If a potential occurs in the fault case,
which is higher than permitted (see Figure 1.6) the Zener
diodes become conducting and the current is conducted away
via the ground. The fuse "blows".

.

Hazardous area

4 mA ... 20mA

transmitter

Figure 1.5 Two-channel Zener barrier

2

Safe area

(+)

24 V

R

M

Hazardous

Safe area

area

Hazardous potential

Hazardous potential

Figure 1.6 Non-grounded Zener barrier

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

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Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

AC/DC
supply
voltage

Fault

Power suppl

Transformer

Hazardous
area

Safe area

Fault

Power supply

Transformer

Fault current

Intrinsically
safe ground

Figure 1.7 Grounded Zener barriers

The system must have its own independent ground
conductor, through which no supply system current
flows.

Date of issue 05/23/03

1.4 Installation notes

Pepperl+Fuchs Zener barriers in the Z7, Z8 and Z9 series can
be mounted on a standard rail to EN 50022 in 3 different
arrangements.

• Equipotential bonding via the standard rail (grounding of all
snapped-on Zener barriers)

Insertion strip
ZH-ES/LB

Label carrier
ZH-Z.BT

DIN rail NS 35/7.5
35 mm standard rail
to DIN EN 50 022

Clamp
ZH-Z.USLKG5

Figure 1.8 Equipotential bonding via the standard rail

• Group grounding through insulated mounting

Mounting block
ZH-Z.AB / NS

Figure 1.9 Insulated mounting (Individual grounding)

• Individual grounding through insulated mounting

Mounting block
ZH-Z.AB/SS

Single socket
ZH-Z.ES

N-Combined rail
ZH-Z.NLS-Cu3/10

Zener barriers - operating instructions

Installation notes

Pepperl+Fuchs Zener barriers also feature a space-saving

12.5 mm housing which incorporates up to 3 channels.

11012.5

115

Figure 1.11 Mechanical features

Construction: Modular terminal housing in Makrolon,
flammability classification UL 94: V -0

Fixing: Snaps onto 35 mm standard rail to DIN EN 50022
Connection options: Self-opening terminals, max. core cross-

section 2 x 2.5 mm²
The barriers are usually installed in racks or control cabinets.

They can be built into housings under production conditions,
with the proviso that the housing must afford adequate
protection. They can also be employed in hazardous areas,
when it has been ascertained that the housing has been
certificated for this purpose.

The installation must be carried out in such a way that the
intrinsic safety is not compromised by the following factors:

• Danger of mechanical damage

• Non-authorised changes or influence exerted by external
personnel

• Humidity, dust or foreign bodies

• Ambient temperature exceeding the permissible level

• The connection of non-intrinsically safe circuits to
intrinsically safe circuits

Grounding of the mounting rail is of the normal type, i. e. both
ends are connected to the intrinsically safe ground. This also
simplifies checking the grounding.

Many installations provide the option of subsequent expansion.
Replacement cable for this purpose can be connected to the
Z799 dummy barrier and unused cable can be connected to
the intrinsically safe ground.

Connector for
ground lead
ZH-Z.AK4

Connector
ZH-Z.AK16

Ground rail feed
ZH-Z.LL

Spacing roller
ZH-Z.AR.125

Figure 1.10 Insulated mounting (Individual grounding)

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

4

Zener barriers - operating instructions

Zener barrier specifications

1.5 Zener barrier specifications

Nominal data

The following are typical data used in the description of a
barrier:
28 V, 300 Ohm, 93 mA. These values relate to the maximum
voltage, the minimum value of the built-in resistance and the
resulting maximum current.

The maximum voltage stated is not representative of the
operating range, it is the maximum value that can be attained
in a failure case, before the fuse responds. The resistance
value is not identical to the maximum series resistance. These
values merely provide an indication of the maximum values
that can apply in the case of a failure.

Series resistance

This is the resistance that can be measured between the two
ends of a barrier channel. It is obtained from the sum of the
resistance R and resistance value of the fuse at an ambient
temperature of 20 °C.

Polarity

Zener barriers are available in various versions. On Zener
barriers for positive polarities the anodes of the Zener diodes
are grounded. On barriers for negative polarities it is the
cathodes which are grounded. On barriers for alternating
polarities, interconnected Zener diodes are employed and one
side is grounded. These can be used for both alternating
voltage signals and direct voltage signals.

Maximum voltage in the intrinsically safe circuit. (U

This is the maximum value of voltage that can occur in the
intrinsically safe circuit in the failure case.

Maximum current in the intrinsically safe circuit (Ik)

)

z

This is the maximum current that can flow in the intrinsically
safe circuit in the failure case.

Maximum input voltage (max. U

)

in

The maximum voltage (correct polarity) that can be applied
between the contacts in the safe area and the ground without
the fuse responding. This value is determined for an open
intrinsically safe circuit and an ambient temperature of 20 °C.

Input voltage (Uin at 10 (1) µA)

The maximum voltage (correct polarity) that can be applied
between the contacts in the safe area and the ground at a
defined leakage current (as a rule 10 µA). This is the upper
value of the recommended operating range.

Maximum connectable external capacitance C

max

This is the maximum capacitance that can be connected to the
terminals of the barrier intrinsically safe circuit. This value is
determined from the sum of the wiring capacitance and the
input capacitance of the field device.

Maximum connectable external inductance L

max

This is the maximum inductance that can be connected to the
terminals of the barrier intrinsically safe circuit. The value is
determined from the sum of the inductance of the wiring and
the input inductance of the field device.

Note:
The designations of the values given in the specifications

above are not those of the relevant standards, but those
specified on certificates of conformity (e. g. in EN 60079-14,
Section 3, IK is now IO).

1.6 How to select the correct barrier

For very many applications the standard solutions are given in
this catalogue, in the section on Example Applications.
However, in the event that a particular application has not been
covered, the following information may be helpful.

1. First decide whether it will be necessary to have a floating
circuit, or whether the intrinsically safe circuit can be
connected directly to ground. Check whether any existing
instrumentation is grounded. If the answer is yes, then
check whether additional grounding could lead to faults.
Bear in mind that the floating circuit offers a better common­mode rejection characteristic than the grounded circuit. On
the other hand, it is more expensive. If a floating circuit is
employed, the barriers will normally resist a ground fault.

2. Select the required polarity. This is either determined by the
circuit itself, or by any other existing grounds in the circuit. In
most applications barriers for positive polarities are used. In
order to achieve greater system standardisation, barriers
suitable for alternating polarities can be used in place of
unipolar ones.

3. Decide the nominal voltage of the Zener barrier. Then
determine the maximum output voltage of the device in the
safe area during normal operation. Normally the required
value is the next highest nominal voltage of a Zener barrier.
If these values are close together, it could be that the

recommended operating range of the Zener barrier is
exceeded. The consequence of this is that the leakage
current will be greater than 10 µA. In this case a barrier with
a higher nominal voltage should be used. The leakage
current is determined for an open intrinsically safe circuit
and this then represents the maximum value at the given
voltage.

4. Take account of the maximum series resistance of the
Zener barrier and its effect on the intrinsically safe circuit.
Make sure that this resistance does not cause an
inadmissibly high loss of voltage. In circuits having high
resistance - usually when voltage signals are being
transferred - this resistance is not relevant. If for example a
barrier has a max. series resistance of 1 kOhm, then the
resulting error is 0.1 %, if the input resistance of the
connected device is 1 MOhm.

5. Check whether or not the field device must be certificated for
use in the hazardous area. If certification is necessary,
check what the prerequisites are for permitting the field
device to be used in connection with a Zener barrier.

6. What is the overall length of the cabling between the voltage
supply and the field device? Note the number of conductors
in the system!

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

5

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

7. The following points have to be clarified if special field
devices are used.

• If the field device is a 4 mA ... 20 mA transmitter: What load
in ohms can be connected to the transmitter so that it can
attain 20 mA as before?

• If the field device is a current/pressure converter: What load
can be connected to the controller card so that it can attain
20 mA as before?

• If the field device is a transmitter: How high is the load in the
safe area? (typically, resistances of up to 250 Ohm are used
in the controller)

Z ...

Zener barriers - operating instructions

How to select the correct barrier

Barrier with replaceable back-up fuse

The introduction of a replaceable back-up fuse ahead of the
integrated fuse provides protection against faults which could
occur during the commissioning of the system. It is always

Type

Channels

Z715.F 1 106 13 13.6 100 63 217,063

Z728.F 1 327 27 28 80 50 217,05

Z728.H.F 1 250 27 28 80 50 217,05

Z765.F 2 106

Z779.F 2 327

Z779.H.F 2 250

Z787.F 2 327

Z787.H.F 2 250

Z960.F 2 64

Z961.F 2 106

Z966.F 2 166

Max. series

resistance

Ohm V V mA mA

106

327

250

36 + 0.9V

25 + 0.9V

64

106

166

Uin

at 10 µA

13

13
27
27

27
27
27

27
27
27

6.5

6.5

6.5

6.5
10
10

arranged that the outer fuse will respond before the inner,
innaccessible fuse. The fuses used are specially intended for
use on barriers.

Uin

max

13.6

13.6
28
28

28
28
28

28
28
28

9.5

9.5

8.1

8.1

11.7

11.7

Fuse rating External fuse Fuse supplied

100

100

80
80

80
80
80

80
80
80

80

80
160

160
100
100

63

63
50
50

50
50
50

50
50
50

50

50
100

100

63

63

by LITTLEFUSE

217,063

217,05

217,05

217,05

217,05

217.05

217.1

217.063

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

6

Zener barriers - operating instructions

How to select the correct barrier

Type Nominal data Ex-characteristics for [EEx ia] IIC Certification no.

+ ve - ve a.c. V W Uz (V) R

Z705

–

Z710

–
–

Z713 Z813 – 15.75 22 15.75 21.8 723 2.84 0.48 0.076 12.5 BAS 01 ATEX 7005

Z715

Z715.F

–

Z715.1K

–

Z722

Z728
Z728.H

Z728.F

Z728.H.F

Z728.CL

–

Z755 Z855 – 5

Z805

–

Z810

–

Z810.CL

Z815

Z815.F

–
–
–

Z822

Z828
Z828.H

Z828.F

Z828.H.F

Z828.CL

–

–

Z905

–

Z910

–

–
–

Z915

–

Z915.1K

–
–
–

–
–
–

Z928

5

5
10

10
10

15
15

15
15
15

22
28
28

28
28
28

28

5

10

4.94

10

4.98

50

9.56

50

9.94

50

9.56

100

14.7

100

14.7

100

15.0

1k

14.7

1k

150
300
240

300
240
300

300

10104.94

4.94

4.94

15

22
28
28

28
28
28

28

(W) IK(mA) P

min

9.8

9.8
49

49
49

98
98

98

980
980

147
301
235

301
235
301

301

9.8

9.8

4.9

504
499
195

203
195

150
150

153

15
15

150

93

119

93

119

93

93

504

504

1008

max

0.62

0.61

0.47

0.50

0.47

0.55

0.55

0.57

0.06

0.06

0.82

0.65

0.83

0.65

0.83

0.65

0.65

0.62

0.62

1.25

(W) C

max

100
100

3

3
3

0.58

0.62

0.58

0.58

0.58

0.17

0.083

0.083

0.083

0.083

0.083

0.083

100

100
100

(µF) L

(mH) L/R Ratio

max

0.14

0.14

0.86

0.86

0.86

1.3

1.45

1.3
144
144

1.45

3.05

1.82

4.21

2.59

3.05

3.05

0.14

0.14

0.03

57

BAS 01 ATEX 7005

57

BAS 01 ATEX 7005

73

BAS 01 ATEX 7005

73

BAS 01 ATEX 7005

73

BAS 01 ATEX 7005

64

BAS 01 ATEX 7005

67

BAS 01 ATEX 7096

64

BAS 01 ATEX 7005

570

BAS 01 ATEX 7005

570

BAS 01 ATEX 7005

45

BAS 01 ATEX 7005

56

BAS 01 ATEX 7005

44

BAS 01 ATEX 7005

55

BAS 01 ATEX 7096

44

BAS 00 ATEX 7096

56

BAS 01 ATEX 7005

56

BAS 01 ATEX 7005

57

BAS 01 ATEX 7005

57
22

– – Z955 5

Z757

–

–

–

Z764 Z864 – 12121k1k11.6

– – Z964 12

Z765

Z765.F

Z857

–

–

–

Z865

Z865.F

–

Z961

Z961.F

Z961.H

–

–

10104.89

5

7

10

7

10

9

100

9

100

9

100

9

100

9

360

9

360

121k1k

15

100

15

100

15

100

15

100

4.89

9.78

7.14

7.14

7.14

17.4

17.4

17.4

11.6

11.6

14.7

14.7

14.7

14.7

14.7

14.7

8.7

8.7

8.7

8.7

8.7

8.7

12
12

24

9.8

9.8

4.9

9.8

9.8

4.9

98
98
98

98
98
98

352.8

352.8
355

980
980

490

980
980

490

98

98
49
98

98
49

499

499
998

729
729

1457

89
89

178

89
89

178

25
25
49

12
12

24

12
12

24

150

150
300
150

150
300

0..61

0.61

1.22

1.3

1.3

2.6

0.19

0.19

0.39

0.192

0.192

0.384

0.05

0.05

0.11

0.03

0.03

0.06

0.04

0.04

0.08

0.55

0.55

1.1

0.55

0.55

1.1

100

100

3.3

13.5

13.5

13.5

4.9

4.9

0.346

4.9

4.9

0.31

4.9

4.9

0.346

1.41

1.41

1.41

1.41

1.41

0.125

0.58

0.58

0.58

0.62

0.62

0.62

0.14

0.14

0.03

0.07

0.07

0.02

4.69

4.69

1.14

4.39

4.39

1.07

57
57

15.2

240
240

61

240
240

61

1.3

1.3

0.32

1.45

1.45

0.32

57

BAS 01 ATEX 7005

57
22

28

BAS 01 ATEX 7005
28
11

182

BAS 01 ATEX 7005

182

72

176

BAS 01 ATEX 7096

176

67

BAS 01 ATEX 7005

613
613
249

1.0

BAS 01 ATEX 7005

1.0

360

1.0

BAS 01 ATEX 7005

1.0

360

64

BAS 01 ATEX 7005

64
22
67

BAS 01 ATEX 7096

67
22

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

7

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

Zener barriers - operating instructions

How to select the correct barrier

Max.

end-to-end

resistance

W VVmA

18.18

18.18
56

56

63 + 2 V

29 13.7 14.6 160

107
119

107
1025
1025

166

327

250

338

261

342 + 2 V

327

18.18

18.18
–

18.18

18.18
–

15.5

15.5
–

106
106

–

113
380

–

380
380

–

1033
1033

–

1033
1033

–

U

in

at 10 µA

0.9 (1 µA)

0.9 (1 µA)

6.5

6.5

6.5

13.0

13.0

13.0

13.0

13.0

19.0

26.5

26.5

26.5

26.5

26.5

26.0

0.9 (1 µA)

0.9 (1 µA)
–

0.9 (1 µA)

0.9 (1 µA)
–

6.0

6.0
–

6.5

6.5
–

6.5

6.5
–

6.5

6.5
–

10.0

10.0

–

10.0

10.0

–

U

max

4.8

4.7

8.9

9.3

8.9

13.6

13.8

14.0

13.6

14.0

20.1

28.0

28.0

28.0

28.0

28.0

27.6

4.8

4.8
–

4.7

4.7
–

6.9

6.9
–

8.1

8.1
–

8.0

8.1
–

8.1

8.1
–

11.0

11.0

–

11.7

11.7

–

in

Fuse rating

250
250
100

100
100

100

63

100
100
100

50
50
80

50
50
50

50

250

250

–

250

250

–

200
200

–

100
100

–

100

50

–

50
50

–

50
50

–

50
50

–

see circuit

diagram No.

1), 2)

3)

1), 2)

3)

1), 2)

1), 2)

3)

3)

1), 2)

1), 2)

1), 2)

Hazardous area Safe area
connections connections

1)

18

CL

x3

27

+VE type

2)

18

CL

x3

27

-VE type

3)

Circuit diagram

1), 2)

3)

4), 5) A1

6) A1

18

x3

x3

27

AC type

4)

18

x3

x3

6

4), 5)

6)

27

3

45

+VE type

5

)

18

27

6)

3

45

4), 5) A1

-VE type

x3

x3

6

6)

6) A1

18

27

x3
x3

see note 2

A2

B

A2

B

A1
A2

B

A1
A2

B

A1
A2

B

A1
A2

B

A2

B

A2

B

107

107

–
119

119

–

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

13.0

13.0
–

13.0

13.0
–

13.6

13.6
–

13.9

13.9
–

100

100

–
63

63

–

4), 5) A1

3

45

AC type

x3
x3

6

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

A2

B
A1

A2

B

8

Zener barriers - operating instructions

How to select the correct barrier

Type Nominal data Ex-characteristics for [EEx ia] IIC Certification no.

+ ve - ve a.c. V W Uz (V) R

– – Z966 1212150

1501212

24

–

–

Z966.F

12
12

150
150

12
12
24

–

–

Z966.H

12
12

75
75

12
12
24

Z772 Z872 – 2222150

1502222

22

Z778

Z878

–

28
28

600
600

28
28

28

Z779

Z879

–

28
28

300
300

28
28

28

Z779.H

Z879.H

–

28
28

240
240

28
28

28

Z779.F

Z779.H.F

Z879.F

Z879.H.F

–

–

28
28

28
28

300
300

240
240

28
28

28
28

(W) IK(mA) P

min

147
147

73.5

164

147
147

73.5

73.5

73.5

36.5

147
147

73.5

164

164
164
328

150
150

300

607
607

303.5
301
301

150.5
235
235

117.5

186
119
119

238
301
301

235
235

120

120

82
82

82
82

46
46

93
93
93

93
93

max

0.24

0.24

0.48

0.24

0.24

0.49

0.49

0.49

0.98

0.82

0.82

1.64

0.32

0.32

0.65

0.65

0.65

1.3

0.83

0.83

1.67

0.65

0.65

0.83

0.83

(W) C

(µF) L

max

max

1.41

1.41

0.125

1.41

1.41

0.125

0.17

0.17

no approval for IIC

0.083

0.083

0.083

0.083

0.083

no approval for IIC

0.083

0.083

no approval for IIC

0.083

0.083

0.083

0.083

(mH) L/R Ratio

5.52

5.52

1.38

1.38

1.38

0.33

1.45

147
147

57

75
75
36

4545BAS 01 ATEX 7005

1.45

17.2

17.2

3.05

3.05

3.05

1.82

1.82

4.21

4.21

2.59

2.59

109
109

42
56
56

44
44

55
55

44
44

BAS 01 ATEX 7005

BAS 01 ATEX 7096

BAS 01 ATEX 7005

BAS 01 ATEX 7005

BAS 01 ATEX 7005

BAS 01 ATEX 7005

BAS 00 ATEX 7096

BAS 01 ATEX 7096

Z796 Z896 – 26.6

Z788

Z788.H

Z788.R

Z888

Z888.H

–

–

–

–

Z786 Z886 28

Z787

Z787.H

Z787.F

Z787.H.F

Z887

Z887.H

Z887.F

Z887.H.F

–

–

–

–

20.5

28
10

28
10

28
10

28

28

28

28

28

28

28

28

28

28

320
415

300

50

240

50

300

50

Diode
Diode

Diode

300

Diode

240

Diode

300

Diode

240

Diode

26.6

20.5

26.6

28

9.56
28

28

9.56

28
28

9.56

28

28
28

28

28

28
28
28

28
28
28

28
28
28

28
28

314
407
177

301

49
42

235

49

40

301

49

42

Diode
Diode

Diode

301

Diode

301
235

Diode

235
301

21.8
301

235.2

14.7

235.2

85
50

135

93
195
288

119
195

314

93
195

288

0
0

0

93

0

93
119

0

119

93

Diode

93
120

Diode

120

0.56

0.26

0.82

0.65

0.47

0.87

0.83

0.47

1.0

0.65

0.47

0.87

0.0

0.0

0.0

0.65

0

0.65

0.83

0

0.83

0.65

0

0.65

0.83

0

0.83

0.094

0.204

0.094

0.083

3.0

0.083

0.083

3.0

0.083

0.083

3.0

0.083

0.083

0.083

0.083

0.083

0.083

0.083

0.083

0.083

0.083

0.083

0.083

0.083

0.083

0.083

0.083

5.14

14.6

2.05

3.05

0.86

0.32

1.82

0.86

0.26

3.05

0.86

0.32

–
–

–

3.05

–

3.05

2.82

see note 1

2.82

4.21

–

4.21

2.59

–

2.59

64

BAS 01 ATEX 7005

138

34

56

BAS 01 ATEX 7005
73
26

44

BAS 01 ATEX 7005
73

25
56

BAS 01 ATEX 7005
73

26

–

BAS 01 ATEX 7005

–

–

56

BAS 01 ATEX 7005

–
56
44

BAS 01 ATEX 7005

44

BAS 01 ATEX 7096

55

–

55

BAS 01 ATEX 7096

44

–

44

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

9

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

Zener barriers - operating instructions

How to select the correct barrier

Max.

end-to-end

resistance

U

in

at 10 µA

U

max

in

Fuse rating

W VVmA

166
166

–

169
169

–

82
82

–

166
166

–

646
646

–
327
327

–
250
250

–
338
338

264
264

340
437

–

327

64

–

250

64

–
327

64

–

36 + 0.9 V
36 + 0.9 V

–

327

36 + 0.9 V

–
250

25+ 0.9 V

–
338

46+ 0.9 V

–
264

39+ 0.9 V

–

10.0

10.0
–

10.0

10.0
–

10.0

10.0
–

19.0

19.0

–

26.5

26.5

–

26.5

26.5

–

26.5

26.5

–

26.5

26.6

26.5

26.5

24.0

18.0
–

26.5

6.5
–

26.5

6.5

–

26.5
–

–

26.5

26.5

–

26.5

26.5
–

26.5

26.5
–

26.5

26.5
–

26.5

26.5
–

11.7

11.7
–

11.9

11.9
–

11.7

11.7
–

20.1

20.1

–

28.0

28.0

–

28.0

28.0

–

28.0

28.0

–

28.0

28.0

28.0

28.0

25.1

19.5
–

28.0

9.1
–

28.0

9.1

–

28.0

9.1

–

28.0

28.0

–

28.0

28.0
–

28.0

28.0
–

28.0

28.0
–

28.0

28.0
–

50
50

–

63
63

–

100
100

–

50
50

–

50
50

–
50
50

–
80
80

–
50
50

50
50

50
50

–

50
50

–

80
80

–
50
50

–

50
50

–

50

50

–
80

80

–
50

50

–
50

50

–

see circuit

diagram No.

6)

6)

4), 5) A1

4), 5)

4), 5)

4), 5)

Hazardous area Safe area
connections connections

4)

18

27

3

45

+VE type

5

)

18

27

3

45

-VE type

x3

x3

x3

x3

6

6

6)

18

27

3

45

AC type

x3
x3

x3
x3

6

7)

Circuit diagram

18

4), 5) A1

4), 5)

4), 5)

27

3

45

AC type

All diodes are turned 180˚

for the -VE version.

x3

x3

6

8)

7)

8) A1

9)

18

27

3

45

All diodes are turned 180˚

for the -VE version.

x3

x3

6

9)

9)

18

27

3

45

All diodes are turned 180˚

for the -VE version.

x3

x3

6

see note 2

A1
A2

B

A1
A2

B

A1
A2

B

A2

B

A1
A2

B
A1
A2

B
A1
A2

B

A2

B

A1
A2

B

A1
A2

B
A1
A2

B

A2

B

A1

A2

B
A1

A2

B
A1

A2

B
A1

A2

B

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

10

Zener barriers - operating instructions

How to select the correct barrier

Type Nominal data Ex-characteristics for [EEx ia] IIC Certification no.

+ ve - ve a.c. V W Uz (V) R

–

–

– – Z965 1515100

– – Z967 1717120

– – Z972 2222300

– – Z978 2828600

– – Z954 4.5

–

–

Z960

Z960.F

10
10

10
10

4.5

4.5

50

9.94

50

9.94

9.94

50

9.94

50

9.94

9.94

1001515

15

16.8

120

16.8

16.8

3002222

22

6002828

28

12

4.5

12

4.5

12

4.5

9.0

9.0

9.0

(W) IK(mA) P

min

49
49

24.5

98
49
49

98
98
49

117
117

58

301
301

150

607

607
304

11.76

11.76

11.76

5.88

3.92

17.64

203
203
406

203
203
406

153
153
306

143
143

286

73
73

146

46

46
93

383

383
383
765

1150

510

max

0.50

0.50

1.0

0.51

0.51

1.02

0.57

0.57

1.14

0.60

0.60

1.20

0.40

0.40

0.80

0.32

0.32

0.65

0.43

0.43

0.43

0.86

1.29

1.15

(W) C

max

3;0
3;0
3;0

2.63

2.63

2.63

0.58

0.58

0.58

0.38

0.38

0.38

0.17

0.17

0.17

0.083

0.083

0.083

100

100
100

4.9

4.9

4.9

(µF) L

(mH) L/R Ratio

max

0.86

0.86

0.19

0.82

0.82

0.82

1.3

1.3

0.29

1.63

1.63

0.24

6.95

6.95

1.45

17.2

17.2

3.05

0.24

0.24

0.24

0.068

0.03

0.12

73

BAS 01 ATEX 7005
73
26

69

BAS 01 ATEX 7096
69
25

64

BAS 01 ATEX 7005
64
20

60

BAS 01 ATEX 7005
60

21

90

BAS 01 ATEX 7005
90

35

109

BAS 01 ATEX 7005

109

42

81

BAS 01 ATEX 7005

81
81
41

27
30

Dummy

Z799

11

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

Zener barriers - operating instructions

How to select the correct barrier

Max.
end-to-end
resistance

W VVmA

64
64

–

–
75
75

115
115

–

136
136

–

327
327

–

646

646

–

U

in

at 10 µA

6.5

6.5
–

–

6.5

6.5

13.0

13.0
–

15.0

15.0

–

19.0

19.0

–

26.0

26.0
–

U

max

9.5

9.5
–

–

9.7

9.7

14.2

14.2
–

16.2

16.2

–

20.9

20.9

–

27.6

27.6
–

in

Fuse rating

50
50

–

–
50
50

50
50

–

50
50

–

50
50

–

50

50

–

see circuit

diagram No.

10)

Hazardous area Safe area
connections connections

10)

Circuit diagram

18

27

3

10) A1

10) A1

45

11)

x3

x3

6

18

x3

10) A1

36

x3

2

7

x3

10) A1

45

see note 2

A1
A2

B

A1
A2

B

A2

B

A2

B

A2

B

A2

B

27.27

27.27

27.27
–

–
–

0.9 (1 µA)

0.9 (1 µA)

0.9 (1 µA)
–

–
–

4.9

4.9

4.9
–

–
–

50

50
50

–

–
–

Note 1:

Zener barriers type Z787H and Z887H have channels with
diode returns.

The Ex-terminals for the channels with diode returns should be
regarded as 28 V voltage sources.

The 28 V must be considered as the theoretical maximum up
to which a capacitive load can be applied to the Ex-terminals
due to the leakage current of the diode return. This voltage is
only used in calculating the load capacitance.

11) A1

A2
A3

18

27

3

6

45

Note 2:

A1, A2 and A3 are separate channels.
B: Two channels in parallel circuit with a ground connection.
C: Two channels in series circuit without a ground return.

B

B
C

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

12

Zener barriers - operating instructions

Application examples

1.7 Application examples

Temperature measurement

Hazardous area

Not grounded

The simplest and most favourably priced solution is a single­channel Zener barrier. It should be noted, however, that the

1

CL

2

Hazardous area

1

2

3

4

Safe area

Z705

8

x3

7

Temperature

monitoring

or control

device is not grounded in the safe area. The system is
approved for [EEx ia] IIC.

Safe area

Z960

8

x3

x3

x3

7

6

5

Temperature

monitoring

or control

The use of a two-channel barrier prevents the direct ground
connection of the intrinsically safe circuit. Grounding only takes
place in the event of a fault, when the Zener diodes conduct.

Hazardous area

1

2

3

4

1

2

3

4

Z961

Z961

This circuit arrangement prevents the occurrence of mutual
interference between the various circuits. The system is
approved for [EEx ia] IIC.

Safe area

8

x3
x3

x3
x3

x3
x3

x3
x3

7

6

5

V

8

7

6

5

The illustration shows the set up for a temperature
measurement with a 4-wire Pt100. None of the 4 wires is
connected directly to ground. The complete system is therefore
"quasi ground-free".

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

13

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

This is the best option when the intention is to suppress the
influence of the end-to-end resistance of the barrier on the
measuring accuracy as far as possible.

Date of issue 05/23/03

Temperature measurement

Zener barriers - operating instructions

Application examples

Hazardous area

Z954

1

3

2

4

The circuit arrangement shows the connection of a Pt100 in 3­wire technology, using the 3-channel Zener barrier Z954. The
whole system is quasi ground-free. All 3 barriers have identical

Hazardous area

1

2

3

4

Z961

Safe area

8

x3

x3
x3

x3

x3
x3

6

7

Test circuit

5

end-to-end resistances, so that the resulting error is restricted
to a minimum. The system is approved for [EEx ia] IIC.

Safe area

8

x3
x3

x3
x3

7

6

5

Z954

1

3

2

4

Z954

1

3

2

4

The circuit consists of a system of a maximum of seven
Pt100s. The Pt100s are connected in series to a constant
current source. Each voltage signal is transferred to a receiver
via a Z954.

8

x3

x3
x3

x3
x3

x3

x3
x3

x3
x3

x3
x3

6

7

5

Receiver with

galvanically

isolated inputs

8

6

7

5

The Z954s have been selected due to their high end-to-end
resistance. Due to the high input resistance of the receiver, the
high end-to-end resistance has practically no effect on the
accuracy of measurement.

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

14

Zener barriers - operating instructions

Application examples

0 mA … 20 mA/4 mA … 20 mA transmitter

Hazardous area

Z728

1

CL

2

If a ground-free power supply is available, the use of a single­channel Zener barrier, grounded in the safe area, represents
the simplest and most economical solution. The ammeter can
be used in combination with a recording instrument, a trip
amplifier, or a 250 Ohm resistance, or replaced by these
devices. In so doing, the overall resistance of the arrangement
must be taken into account. The working range of the barrier

Hazardous area

Z788

1

2

Safe area

8

x3

7

A

caters for an input voltage of up to 27 V. For each built-in
250 Ohm resistance the output voltage of the power supply
can be increased by 1 V. By using a 250 Ohm resistance and a
supply voltage of 28 V, a source of 16.5 V at 20 mA is available
to the transmitter in the hazardous area. The internal voltage
drop across the barrier is then 6.5 V. The system is approved
for [EEx ia] IIC.

Safe area

8

x3

7

3

4

With this 2-channel Zener barrier, it is possible to supply a
number of circuits with one source. All the wiring is quasi
ground-free. The maximum voltage supply is 27 V. The internal
voltage drop across the barrier is 7.8 V at 20 mA, so that

19.2 V are available for the field device and ammeter. If the

6

x3

5

A

ammeter for converting the current signal into a 1 V … 5 V
voltage signal is replaced by a 250 Ohm resistance, then

14.2 V are available at the field device. The system is
approved for [EEx ia] IIC.

15

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

0 mA … 20 mA/4 mA … 20 mA transmitter

Zener barriers - operating instructions

Application examples

Hazardous area

Z788.R

1

2

3

4

This system can be used if the field device requires a relatively
high voltage. A 250 Ohm resistance is connected in parallel
with the Ex-output of the 10 V/50 Ohm output of this 2-channel

Hazardous area

Z787

1

2

3

4

x3

Safe area

8

x3

x3

7

6

5

V

barrier. Thus a voltage of 15.5 V is available at the field device
if the voltage supply is 27 V. The system is approved for
[EEx ia] IIC.

Safe area

8

x3

x3

7

6

5

A

The combination of a 28 V, 300 Ohm and a 28 V barrier with
diode return is the solution for applications with 3-wire
transmitters. Special attention must be paid here to the internal

voltage drop. The reason for this is the diode return. The
system is approved for [EEx ia] IIC.

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

16

Zener barriers - operating instructions

Application examples

SMART transmitter

Hazardous area

Z787

1

2

3

4

The simplest possible solution is the use of a 2-channel Zener
barrier with 28 V, 300 Ohm and 28 V diode return. If a
regulated power supply unit provides an output voltage of 27 V,

13.9 V will be available to the transmitter and wiring in the Ex­area.

Strain gauge bridges

Hazardous area

1

2

Z966

Safe area

8

x3

x3

7

6

5

A

The data transfer is bidirectional, so that a non-certificated
communicator can be connected and used in the the safe area.
The system is approved for [EEx ia] IIC.

Safe area

8

x3
x3

7

3

4

1

2

3

4

1

2

3

4

Z964

Z964

x3
x3

x3
x3

x3
x3

x3
x3

x3
x3

6

5

8

7

6

5

8

7

6

5

+

-

Signal

The strain gauge bridge is supplied via the Z966. The Z966
enables a 350 Ohm strain gauge bridge to be supplied with
8 V. The voltage feedback via the Z964 can be dispensed with,
although in practice most applications require this feedback to

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

17

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obtain the best possible accuracy of measurement.
The millivolt signal is transferred to the safe area via the Z964.

The system is approved for [EEx ia] IIC.

Date of issue 05/23/03

Wire strain gauges

Zener barriers - operating instructions

Application examples

Hazardous area

350 Ohm

350 Ohm

Z966

1

x3

Z966

Z964

x3

x3
x3

x3
x3

x3
x3

x3
x3

x3
x3

2

3

4

1

2

3

4

1

2

3

4

8

7

6

5

8

7

6

5

8

7

6

5

Sensor +

Sensor -

-0+

Safe area

350 Ohm

1

2

3

4

Z964

If more than one strain gauge bridge is to be supplied from a
common power supply (in the example shown above there are
three), a possible solution is to supply them via two Z966s, as
shown.

8

x3
x3

x3
x3

7

6

5

Both channels of these Zener barriers are arranged in parallel
in order to reduce the end-to-end resistance. This arrangement
provides 8 V to the bridges if the voltage supply is 20 V. The
system is approved for [EEx ib].

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

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18

Zener barriers - operating instructions

Application examples

Potentiometric position detection

Hazardous area

1

2

3

4

Applications in which the accuracy is not critical can be
satisfied as shown above. The intrinsically safe circuit has a
direct connection to ground. An additional resistance on this

Harzardous area

1

x3

Z715

CL

Safe area

Z960

8

x3

x3

7

6

5

V

side would have an effect on the voltage signal and would have
to be taken into account. The system is approved for [EEx ia]
IIC.

Safe area

8

x3

2

Z715.1K

1

CL

x3

2

Z715.1K

1

CL

x3

2

7

8

7

Signal

8

7

If greater accuracy is required, a 4-wire solution must be
applied. The Z715 Zener barrier transfers the power supply to
the potentiometer, whilst two Z715.1K barriers transfer the

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

19

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signal to the receiver. The supply voltage in the example above
could be 13 V.

Date of issue 05/23/03

Solenoid valves

Zener barriers - operating instructions

Application examples

Hazardous area

Z728

1

CL

2

The simplest and most economical solution is a single channel
Zener barrier, with the power supply grounded on its safe side.
If the valve requires 30 mA at a minimum 12 V, then at a

Hazardous area

Z787

1

4

3

2

Safe area

8

x3

7

supply voltage of 27 V, 4 V would remain for the voltage drop
through the field wiring. The system is approved for
[EEx ia] IIC.

Safe area

8

x3

x3

5

6

7

If the switch is in parallel circuit with the nominal mains voltage,
it is usual to use a barrier combination of 28 V, 300 Ohm and a
28 V diode return. In this solution, special attention has to be

Switch status

Hazardous area

Z787

1

4

3

2

In the traditional method of switch status detection, the switch
is provided with noble metal contacts suitable for low voltages
and currents. A ground fault in any field wire leaves the relay in
the de-energised state, despite the switch being closed. This
problem is solved by the use of quasi ground-free wiring.

Z887

paid to the voltage drop in the barrier, since the diode return
causes an additional loss of voltage. The system is approved
for [EEx ia] IIC.

Safe area

8

x3

x3

At a nominal voltage of up to 27 V, a typical coil with 12 V and
approx. 350 Ohm can be used to match the power. The Zener
barrier is approved for [EEx ia] IIC. Negative polarities can be
accommodated with the Z887.

5

6

7

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

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20

Zener barriers - operating instructions

Application examples

Pulse transmission and flow measurement

Hazardous area

Z728

Flow meter with
pulse output

1

CL

2

The simplest method of flow measurement, with or without a
pre-amplifier, is illustrated in the circuit above. The flow meter
sensor generates voltage or current pulses, which are
transmitted to the safe area via the Z728. If the sensor

Hazardous area

Flow meter with
pulse output

1

4

3

2

Z787

Safe area

8

x3

7

Output

generates sinusoidal signals, e. g. an inductive sensor, a Zener
barrier for alternating polarities can be used, for example the
Z928. The Zener barrier is approved for [EEx ia] IIC.

Safe area

8

x3

x3

5

6

7

Output

If the power supply to the flow meter is provided via a 28 V,
300 Ohm barrier and ground, the signal can be transferred via
the diode return of the Z787. When selecting the receiver

LED display

Hazardous area

Z728

1

CL

2

The simplest and most economical solution is the single­channel Zener barrier shown above. The nominal supply
voltage is sufficiently low that the end-to-end resistance of the

(counter), consideration must be given to the fact that the high
signal is damped by the diode. The system is approved for
[EEx ia] IIC.

Safe area

8

x3

7

barrier limits the flow of current through the LED to an
acceptable value. Otherwise a current-limiting resistor is
required. The system is approved for [EEx ia] IIC.

21

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

LED display

Zener barriers - operating instructions

Application examples

Hazardous area

Z728.CL

1

CL

2

The circuit shown above does not require a current limiting
resistor, since the Z728.CL limits the current electronically to a
maximum of 40 mA. At a supply voltage of 18 V … 27 V a
current of 40 mA flows in the intrinsically safe circuit. This

Smoke and fire alarms

Hazardous area

Z728

1

CL

Safe area

8

x3

7

current reduces at lower nominal supply voltages. To special
order, the Z728.CL can be supplied with lower current-limiting
values. The system is approved for [EEx ia] IIC. The Z828.CL
is also suitable for negative polarities.

Safe area

Output

8

I

2

The simplest and most cost-effective solution is shown in the
illustration above. With a 24 V nominal supply voltage, there is
an off-state current of approx. 4 mA. When the detector
responds, the current increases to approx. 25 mA or greater.

Hazardous area

Z787

1

I

4

3

2

x3

7

The current applied to the detector is sufficient to operate the
LED display with sufficient brightness. The system is approved
for [EEx ia] IIC.

Safe area

Output

8

x3

x3

5

6

7

The system shown above is comparable to the Z728 and is
also relatively inexpensive. The Z787 is a 2-channel device. In

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com

this application the intrinsically safe circuit is quasi ground-free.
The system is approved for [EEx ia] IIC.

22

Zener barriers - operating instructions

Application examples

Audible alarms

Hazardous area

1

CL

2

Audible alarms operate at relatively high voltages and low
currents. They are approved for use with various Zener

I/P converters

Hazardous area

1

P

I

2

3

4

Z728

Z787

Safe area

8

x3

7

barriers. The simplest solution is the circuit shown above.

Safe area

8

x3

x3

7

6

5

The simplest and most cost-effective solution is a single­channel Zener barrier. The nominal supply control voltage
must either be ground-free or connected to the negative output
to earth. In theory, the field circuit can have a resistance of

900 Ohm if the voltage supply is 27 V. In practice, however, the
voltage values are lower, so that the field circuit normally has a
resistance of 300 Ohm.

23

Date of issue 05/23/03

Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany

Pepperl+Fuchs Group • Tel.: Germany [phone] • USA [phone] • Singapore [phone] • Internet http://www.pepperl-fuchs.com