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circuit Action by 6 8812 E I2:C100 © BSI 28 August
1002−80 ISB © 2001 Table B.4 ( continued ) BS IEC 61882:2001 43
34 Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI No.
11 Element Guide
word Deviation Possible causes Consequences Safeguards Activities
personnel NO No alarm
sounded Sound equipment
failure Personnel not
alerted Dual PA system Cable damage Dual cabling Comments Actions
None Action by 6 8812 E
BS IEC 61882:2001 I2:C100 44
Table B.4 ( continued ) Unlikely Dual power supplies
MORE More alarm Sound equipment
too powerful Personnel suffer
ear damage Sound equipment rated
to not exceed safe level None 13 LESS Less alarm Sound too weak Some personnel
not alerted None Ensure system
15 dB above
background 14 AS WELL
AS As well as
transmit Distortion of
or echoes Lack of clear-cut
personnel None Investigate
engineering 15 PART OF Part of alarm
transmit Alarms but
inadequate No signal to
personnel 16 REVERSE Reverse
transmit As for less alarm
See comments above
reverse initiations and
"all clear" – 78 – 12 © BSI 28 August 2001
1002−80 ISB © Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI No. Element Guide
word Deviation Possible causes Consequences Safeguards Comments Actions
required 17 OTHER
THAN Other than
transmit System initiates
mistake None Review signal
logic so that
PAPA can only
after GPA 18 SOONER Alarm and
soon GPA initiated
disruption of work None Establish clear
personnel 19 LATER Alarm and
late GPA initiation
action Some personnel
may be trapped or
forced to use
route None Action by 6 8812 E I2:C100 © BSI 28 August
1002−80 ISB © 2001 Table B.4 ( continued) Clear
above – 98 – BS IEC 61882:2001 45
54 BS IEC 61882:2001
6 1882 Ó I EC:2001 B.5 – 47 – Piezo valve control system Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI The piezo valve control system (see simplified Figure B.3) shows how HAZOP can be applied
to a detailed electronic system.
A piezo valve is a valve driven by a piezo ceramic. The ceramic element is electrically driven
and lengthens itself in the charged state. A charged piezo ceramic closes the valve.
A discharged piezo ceramic opens the valve. If the piezo ceramic does not lose or gain
charge, the state of the valve is kept.
The system sprays a flammable and explosive liquid into a reaction vessel (not shown). The
overall system with reactor vessel, pipes, pumps, etc. is part of a separate HAZOP study.
Here only the application of a HAZOP study to an electronic unit is shown.
The operation of the unit is a two-state process designed to close the valve on demand,
“state 1”, and open it on demand, “state 2”.
An electrical charge from capacitor C1 is conducted via the transistor T1 to the coupling
capacitor C2 and via the power wire to the piezo valve to close it. In this case transistor T2
and the protection transistor T3 are closed (high resistance).
Capacitor C2 is discharged by transistor T2 to open the valve. To prevent asymmetric
charging of the piezo valve, for example by mechanical or thermal stress, transistor T4
connects the low side to ground.
An electrical shield around the twisted wires of the cable prevents electro-magnetic influences
from effecting the valve. 46
64 © BSI 28 1002−80ISB ©
August 2001 BS IEC 61882:2001
6 1882 Ó I EC:2001 – 48 – Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI Control unit AC/DC
converter T1 charge Cable
C2 D1 Piezo
High D2 Low C1 Shield T2 discharge
Ground T3 protection D3 T4 D4
R IEC 455/01 Figure B.3 – Piezo valve control system © BSI ISB ©
1002−8028ISB © 2001 47
74 BS IEC 61882:2001
6 1882 Ó I EC:2001 – 49 – Description of state 1: c lose valve
Part considered: c able from AC/DC converter and from capacitor C1 via transistor T1,
diode D1, capacitor C2 to the power side of the valve and from the ground side of the valve
via transistor T4 and resistor R to ground. Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI Description of state 2: o pen valve
Part considered: c able from power side of valve via transistor T3, diode D3 and resistor R to
The design intent is as follows.
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This note was uploaded on 09/15/2011 for the course ECON 102 taught by Professor Calvin during the Winter '11 term at Oxford Brookes.
- Winter '11