Penggunaan hp dengan fasilitas sms sudah bukan barang asing lagi, hampir semua
orang sudah memanfaatkannya untuk mengirimkan pesan pendek. Proses sms sederhana
saja, dengan mengetikkan pesan dilayar, send ke nomor yang dituju, sampailah
(berharap), atau tidak sampai jika ada gangguan atau terlambat diterima.
Alarm via SMS
Bagaiman jika hp digunakan untuk kendali atau monitoring jarak jauh, mirip
remote control tv?,apa yang bisa dikendalikannya ?, atau dimonitor?, ambil contoh kasus
berikut ini; mobil yang sudah dilengkapi dengan alarm, lalu alarm berbunyi, bisa saja ada
maling atau hanya kesalahan alarm semata, semuanya menimbulkan suara alarm, orang
disekitar biasanya acuh tak acuh dan menganggap itu adalah alarm palsu atau kesalahan
alarm, bukan maling. Jika pemiliknya jauh dari mobil, bisa jadi alarm bunyi terus
menerus ditempat itu atau maling lebih pintar, sudah bisa mematikan alarm dan
membawa kabur mobil. Bagaimana jika mobil bisa kirim sms ke pemiliknya bahwa ada
maling atau kesalahan alarm?, lalu siapakan yang mengirimkan sms tersebut ?, tulisan ini
akan membahas bahwa hal itu dimungkinkan dengan menggunakan perangkat
mikrokontroler dan hp yang mudah didapat dipasaran.
Sebenarnya aplikasi tidak hanya alarm mobil saja, masalah lain misalnya saat ini
sering terdengar berita tentang pembobolan toko yang ditinggal pergi pemiliknya, tidak
dijaga, atau juga sekolah yang kehilangan beberapa set komputer dengan dibobolnya
ruang komputer tanpa berpenjaga. Seandainya dilengkapi dengan alarm sms ini bisa
dilaporkan melalui sms bahwa toko sedang dibobol, pelaporan dapat ke pemilik, satpam
atau ke polisi, sehingga bisa dilakukan tindakan yang lebih cepat.
Akusisi Data
Istilah akusisi data adalah mengirimkan dan mengambil data dari perangkat, bisa
remote jarak jauh. Remote melalui sms bisa jarak jauh bahkan melampaui batas negara,
selama masih ada jaringan GSM, Melalui HP dapat dikendalikan peralatan ditempat lain,
misalnya menyalakan AC, menghidupkan pompa, lampu, atau melihat status / data
temperatur, tekanan, jumlah pengunjung dan sebagainya dari jarak jauh. Dengan
teknologi hp berkamera, dimungkinkan mengambil gambar dari jarak jauh, untuk
mengetahui suasana ditempat lain, ini juga bisa digunakan untuk sistem keamanan.
Mikrokontroller
Tentu saja ditempat remote harus ada hp dan sim card untuk mengirimkan sms,
lalu siapa yang mencet-mencet hp untuk mengirim sms?, bukan orang tetapi perangkat
komputer yang dihubungkan dengan hp, yang dapat memerintahkan mengirim sms atau
membaca sms, sistem komputer yang dihubungkan dengan hp ini sudah banyak
digunakan untuk kuis-kuis interaktif di tv via sms atau polling via sms, jadi operator
(manusia) tidak perlu repot-repot membaca sms dan menghitung hasil polling. Alat yang
sama digunakan untuk mengases informasi prestasi akademik via sms bagi mahasiswa
perguruan tinggi yang melengkapi sistem informasi akademiknya dengan akses sms.
Komputer tidak akan laik jika digunakan di mobil, ditoko atau di industri yang harus
bekerja 24 jam, karena akan terlalu mubasir, terlalu besar. Solusi yang paling tepat adalah
dengan menggunakan mikrokontroler, semacam MCS51 (Intel), AT89C (Atmel), PIC
(Microchip), 68HC11 (Motorla) atau yang lain. Mikroprosesor adalah otak dari
komputer, jadi sebenarnya mikrokontroler adalah komputer mini yang didisain khusus
untuk instrumentasi dan kendali. Selain harganya murah dan sedikit komponen yang
digunakan dan catu daya rendah akan menguntungkan karena sedikit kemungkinan
terjadi gagal.

Beberapa jenis hp, seperti Nokia, Siemens dan Sony memiliki modem (modulation –
demodulation), seperti juga komputer yang memiliki modem untuk mengirimkan data
melalui jaringan telepon. Jadi hp yang memiliki modem akan bisa dikoneksikan ke
komputer melalui kabel data (RS232 atu USB), sehingga dapat berfungsi sebagai
pengirim data, misalnya sebagai fax. Untuk penggunaan mikrokontroler juga
dikoneksikan melalui kabel data dan mikrokontroler akan berkomunikasi dengan hp
melalui kabel ini. Perintah standart modem dikenal dengan istilah AT Command,
perintah ini dapat digunakan untuk mengirim, menerima/membaca dan menghapus sms,
disamping banyak fungsi lagi. Beberapa jenis hp memiliki extended AT Command yang
bisa digunakan untuk mengambil informasi jenis, model hp, nomor IMEI (Internasional
Mobile Station Equipment Identity) , SIM IMSI (Subscriber Identification Number ),
status batere, kekuatan sinyal, nama operator, lokasi dan cell ID.
Format SMS
Jika kita mengirimkan pesan pendek, pesan ini tidak dikirimkan dalam format
yang tertulis, tetapi harus dikonversi lagi menjadi format PDU (Protocol Data Unit)
semacam kompresi data (pemampatan data), selain pesan tersebut, juga ikut dikirimkan
informasi nomor pengirim, nomor penerima, nomor sms center, tanggal dan jam.
Dipenerima format PDU harus dikembalikan lagi menjadi format text yang bisa dibaca
sesuai pesan yang dikimkan, format PDU berupa pergeseran data-data dari format 7 bit
menjadi 8 bit.
Sensor dan aktuator
Sensor akan memberitahukan kepada mikrokontroler bahwa ada sesuatu yang
berubah, misalnya ada orang masuk ruangan atau mobil, ada kebakaran dsb,
mikrokontroler akan berlaku seperti orang mengirim sms dengan adanya perubahan
tersebut atau menggerakkan aktuator berupa alarm, lampu dsb. Aktuator juga dapat
diaktifkan melalui perintah sms, misalnya untuk mengisi batere, menyalakan ac, lampu
dsb.
Sensor yang paling sederhana adalah saklar on-off, dapat dipasang dipintu, jika
pintu dibuka, saklar berubah status. Sensor keberadaan orang adalah PIR (Pyroelectric
Infra Red), yang mendeteksi adanya objek panas yang bergerak (manusia mengeluarkan
panas infra merah), sensor ini banyak digunakan untuk lampu keamanan, jika ada orang
lewat, lampu menyala. Ultrasonic radar juga merupakan salah satu sensor untuk
mendeteksi adanya objek lain (perubahan objek), ini prinsipnya seperti radar. Sensor lain
dapat berupa fire detector (mendeteksi adanya api), smoke detector (asap), tekanan dan
masih banyak lagi.
Deteksi Posisi
Sistem remote sms ini yang dilengkapi dengan GPS (Global Positioning System),
sebuah perangkat yang harganya juga tidak mahal, menerima sinyal dari satelit dan
melaporkan posisi dimana GPS ini berada, baik lintang, bujur maupun ketinggian.
Sebuah kendaraan dapat dimonitor secara jarak jauh sedang berada dimana dengan cara
ini. Sebenarnya tanpa GPS pun juga dapat dimonitor, karena bisa diketahui cell id dan
location, tetapi tidak setepat menggunakan GPS, karena informasi lokasi dalam cakupan
satu cell yang radiusnya sekitar 2-3 km.
Beberapa kelemahan
Yang jelas harus membayar setiap kali mengirim sms, juga kartu memiliki masa
aktif dan kadang sms terlambat atau malah tidak sampai, masalah ini dapat diatasi dengan
menggunakan kartu yang sejenis, sehingga sms dapat segera sampai.

Compressor & Turbine

Effect of an Inefficient Compressor and Turbine
Frictional losses in the compressor raise the output temperature. Similarly the losses in the turbine
raise the exhaust temperature. These losses are quantified by modifying the temperatures T2 and T4
to account for their increases.
The compression ratio (P2/P1) of the compressor is usually given by the manufacturer and
therefore the temperature of the air leaving the compressor is easily found from (2.13). If the efficiency
of compression ηc is known e.g. 90% and that of the turbine ηt is known e.g. 85% then a better
estimate of the output energy can be calculated. In this situation T2 becomes T2e and T4 becomes
T4e, as follows:-
T2e = T2
ηc
+
1 − 1
ηc
T1 and T4e = T4ηt + (1 − ηt)T3 (2.18)
These would be the temperatures measurable in practice. In (2.14) and (2.15) the pressure
ratios are theoretically equal, and in practice nearly equal, hence:
T2
T1
= T3
T4
= rp
β (2.19)
Where rp is the pressure ratio
P2
P1
or
P3
P4
In practice the temperatures T1 and T3 are known from the manufacturer or from measuring
instruments installed on the machine. The pressure ratio rp is also known. The ratio of specific heats
is also known or can be taken as 1.4 for air. If the compressor and turbine efficiencies are taken into
account then the practical cycle efficiency ηp of the gas turbine can be expressed as:
ηp = T3(1 − rp
δ)ηcηt − T1(rp
β − 1)
T3ηc − T1(rp − 1 + ηc)
(2.20)
which has a similar form to (2.17) for comparison.
2.2.1.1 Worked example
A light industrial gas turbine operates at an ambient temperature T1 of 25◦C and the combustion
temperature T3 is 950◦C. The pressure ratio rp is 10.
If the overall efficiency is 32% find the efficiency of the compressor assuming the turbine
efficiency to be 86%.
From (2.20),
T1 = 273 + 25 = 298◦K
T3 = 273 + 950 = 1223◦K
rp
δ = 10−0.2857 = 0.51796 and rp
β = 10+0.2857 = 1.93063
Therefore,
ηp = 0.32 = 1223(1.0 − 0.51796)ηc(0.86) − 298(1.93063 − 1.0)
1223ηc − 298(1.93063 − 1.0 + ηc)
Transposing for ηc results in ηc = 0.894. Hence the compressor efficiency would be 89.4%.
2.2.2 Maximum Work Done on the Generator
If the temperatures T2e and T4e are used in (2.11) to compensate for the efficiencies of the compressor
and turbine, then it is possible to determine the maximum power output that can be obtained as a
function of the pressure ratio rp.
The revised turbine work done Ute is,
Ute = Cp(T3 − T4)ηt kJ/kg (2.21)
The revised compressor work done Uce is,
Uce = Cp(T2 − T1)
1
ηc
kJ/kg (2.22)
The revised heat input from the fuel Uf e is,
Uf e = Cp(T3 − T2e) kJ/kg (2.23)
where,
T2e = T1
rp
β − 1 + ηc
ηc

From (2.19),
T4 = T3rp
δ (2.24)
and
T2 = T1rp
β (2.25)
Substituting for T2, T2e and T4 gives the resulting output work done Uoute to be,
Uoute = Ute − Uce = Cp(T3 − T3rp
δ)ηt − Cp
T1rp
β − T1
ηc

= Cp T3(1 − rδ)ηt − T1
ηc
(rp
β − 1) kJ/kg (2.26)
To find the maximum value of Uoute differentiate Uoute with respect to γp and equate the result
to zero. The optimum value of γp to give the maximum value of Uoute is,
rpmax =
T1
T3ηcηt
d
(2.27Where
d = 1
2δ
which when substituted in (2.26) gives the maximum work done Uoutemax.
2.2.2.1 Worked example
Find rpmax for the worked example in sub-section 2.2.1.1.
Given that,
T1 = 298 K, T3 = 1223◦C,
r = 1.4, ηt = 0.86 and ηc = 0.894
d = γ
2(1 − γ )
= 1.4
2(1.0 − 1.4)
= −1.75
rpmax =  298
1223(0.894)(0.86)

−1.75
= 0.3169−1.75 = 7.4
2.2.3 Variation of Specific Heat
As mentioned in sub-section 2.2 the specific heat Cp changes with temperature. From Reference 4,
Figure 4.4, an approximate cubic equation can be used to describe Cp in the range of temperature
300 K to 1300 K when the fuel-to-air ratio by mass is 0.01, and for the air alone for compression, as
shown in Table 2.1. The specific heat for the compressor can be denoted as Cpc and for the turbine
Cpt . The appropriate values of Cpc and Cpt can be found iteratively from the cubic expression and
equations (2.24) and (2.25). At each iteration the average of T1 and T2 can be used to recalculate Cpc,
and T3 and T4 to recalculate Cpt . The initial value of γ can be taken as 1.4 in both cases, and Cv
can be assumed constant at 0.24/1.4 = 0.171 kcal/kg K. The pressure ratio is constant. Having found
suitable values of Cpc and Cpt it is now possible to revise the equations for thermal efficiency ηpa
and output energy Uoutea, where the suffix ‘a’ is added to note the inclusion of variations in specific
heat Cp.
Table 2.1. Specific heat Cp as a cubic function of absolute temperature
K in the range 373 K to 1273 K Cp = a + bT + cT 2 + dT 3
Fuel-air Cubic equation constants
ratio
a × 100 b × 10−4 c × 10−7 d × 10−10
0.0 0.99653 −1.6117 +5.4984 −2.4164
0.01 1.0011 −1.4117 +5.4973 −2.4691
0.02 1.0057 −1.2117 +5.4962 −2.5218
The energy equations for the compressor and turbine become,
Ucea = Cpc(T2 − T1)
1
ηc
 kJ/kg (2.28)
and
Utea = Cpt (T3 − T4)
1
ηt
 kJ/kg (2.29)
Also assume that the specific heat Cpf of the fuel–air mixture is the value corresponding to
the average value of T2 and T3, see Reference 4, sub-section 4.7.1, (2.23).
Hence the fuel energy equation becomes, from (2.23),
Uf ea = Cpf (T3 − T2ea) kJ/kg (2.30)
Where
T2ea = T1(rp
βc − 1 + ηc)
ηc
(2.31)
Where rc and rt apply to the compressor and turbine and are found from Cpc, Cpt and Cv.
The work done on the generator is now,
Uoutea = Cpt T3(1 − rp
δt )ηt − CpcT1
ηc
(rp
βt − 1) (2.32)
and
T4ea = T3(ηt rp
δc + 1 − ηt )
From Uf ea and Uoutea the thermal efficiency ηpa can be found as,
ηpa = Uoutea
Uf ea
(2.33)

Gas Turbine Driven Generators

2.1 CLASSIFICATION OF GAS TURBINE ENGINES
For an individual generator that is rated above 1000 kW, and is to be used in the oil industry, it
is usual practice to use a gas turbine as the driving machine (also called the prime mover). Below
1000 kW a diesel engine is normally preferred, usually because it is an emergency generator running
on diesel oil fuel.
Gas turbines can be classified in several ways, common forms are:-
• Aero-derivative gas turbines.
• Light industrial gas turbines.
• Heavy industrial gas turbines.
2.1.1 Aero-derivative Gas Turbines
Aircraft engines are used as ‘gas generators’, i.e. as a source of hot, high velocity gas. This gas is
then directed into a power turbine, which is placed close up to the exhaust of the gas generator. The
power turbine drives the generator. The benefits of this arrangement are:-
• Easy maintenance since the gas generator can be removed as a single, simple module. This can be
achieved very quickly when compared with other systems.
• High power-to-weight ratio, which is very beneficial in an offshore situation.
• Can be easily designed for single lift modular installations.
• Easy to operate.
• They use the minimum of floor area.
The main disadvantages are:-
• Relatively high costs of maintenance due to short running times between overhauls.
• Fuel economy is usually lower than other types of gas turbines.
• The gas generators are expensive to replace.Aero-derivative generators are available in single unit form for power outputs from about
8 MW up to about 25 MW. These outputs fall conveniently into the typical power outputs required
in the oil and gas production industry, such as those on offshore platforms.
2.1.2 Light Industrial Gas Turbines
Some manufacturers utilize certain of the advantages of the aero-derivative machines, i.e. high powerto-
weight ratio and easy maintenance. The high power-to-weight ratios are achieved by running
the machines with high combustion and exhaust temperatures and by operating the primary air
compressors at reasonably high compression ratios i.e. above 7. A minimum of metal is used and so
a more frequent maintenance programme is needed. Easier maintenance is achieved by designing the
combustion chambers, the gas generator and compressor turbine section to be easily removable as a
single modular type of unit. The ratings of machines in this category are limited to about 10 MW.
2.1.3 Heavy Industrial Gas Turbines
Heavy industrial gas turbines are usually to be found in refineries, chemical plants and power utilities.
They are chosen mainly because of their long and reliable running times between major maintenance
overhauls. They are also capable of burning most types of liquid and gaseous fuel, even the heavier
crude oils. They also tend to tolerate a higher level of impurities in the fuels. Heavy industrial
machines are unsuitable for offshore applications because:-
• Their poor power-to-weight ratio means that the structures supporting them would need to be much
larger and stronger.
• Maintenance shutdown time is usually much longer and is inconvenient because the machine must
be disassembled into many separate components. A modular concept is not possible in the design
of these heavy industrial machines.
• The thermodynamic performance is usually poorer than that of the light and medium machines.
This is partly due to the need for low compression ratios in the compressor.
They do, however, lend themselves to various methods of heat energy recovery e.g. exhaust
heat exchangers, recuperators on the inlet air.
Figures 2.1 and 2.2 show the relative costs and weights for these types of machines.
2.1.4 Single and Two-shaft Gas Turbines
There are basically two gas turbine driving methods, known as ‘single-shaft’ and ‘two (or twin) shaft’
drives. In a single-shaft gas turbine, all the rotating elements share a common shaft. The common
elements are the air compressor, the compressor turbine and the power turbine. The power turbine
drives the generator.
In some gas turbines, the compressor turbine and the power turbine are an integral component.
This tends to be the case with heavy-duty machines.
The basic arrangement is shown in Figure 2.3.

Grounding Route

Kita harus membagi grounding menjadi beberapa tipe grounding, yaitu:
1. Signal Ground
Signal Ground harus berpusat pada Main Device (Controller, FF Host, DCS, PLC, dsb.), dimana Main Device dihubungkan ke Earth. Semua Field Device floating (shield drain wire tidak dihubungkan ke device itu sendiri - seperti dikatakan Pak Setyohadi dibawah), tetapi pada setiap junction box / marshalling semua shield drain wire harus tetap dihubungkan yang pada akhirnya drain wire akan terhubung ke Earth di Main Device.
2. Power Ground
Power Ground harus berpusat pada Power Generating Device, dimana Neutral dihubungkan ke Earth.
3. Body Ground
Panel / Enclosure body harus dihubungkan ke Earth terdekat (local) untuk melindungi personel yang bekerja disekitar panel / enclosure agar tidak terkena electric shock. Kalau kita menggunakan Surge Protector, ground juga harus dihubungkan ke local earth. Surge Protector adalah isolated dan baru membuang energinya pada ambang batas tegangan tertentu, dan device diproteksi dengan fuse.

Ketiga tipe ground tersebut harus isolated (tidak saling dihubungkan satu dengan yang lain), karena masing-masing mempunyai earth point sendiri. Menghubungkan satu atau lebih tipe ground diatas bisa menyebabkan ground loop karena akan terjadi multiple earthing. Sebagai standard (semua standard), panel / enclosure harus mempunyai 3 jenis ground bar, dimana Body Ground attached padapanel / enclosure body, sedangkan dua ground bar lainnya harus isolated.

Menjawab pertanyaan Mas Setyohadi, ketiga tipe ground tersebut harus dipisah / isolated satu terhadap yang lain (resistansi sebesar mungkin); Resistansi Earth sekecil mungkin. Memang agak membingungkan kalau kita bekerja di Power Generating Plant, seperti pengalaman saya di Pembangkit Kamojang, disitu hanya ada satu ground yang di-asumsi = earth, jadi ketiganya disatukan. Ukuran Ground cable juga harus diperhatikan current carrying capacity-nya agar tidak panas atau menjadi fuse; untuk signal ground, standard drain wire dari signal cable sudah cukup karena tujuannya adalah membuang potential dari EMI dan RFI; sedangkan untuk Power Ground dan Body Ground (terutama apabila menggunakan surge protector), kA rating harus diperhitungkan.

Sebagai tambahan:
Khusus untuk signal dengan frekwensi tinggi - orde MHz ~ GHz, seperti Ethernet 100/1000BaseTx (copper screened/shielded twisted pair), grounding diperlakukan secara khusus. Kalau pada butir 1 diatas (low frequency) field end harus floating, pada frequency tinggi setiap ujung shield/screen harus grounded, karena pada frequency tinggi shield/screen menjadi semacam antenna dan akan timbul standing wave. Umumnya high frequency signal cable jaraknya tidak terlampau panjang, sehingga kita bisa memasang grounding grid (anyaman bujur sangkar) yang dihubungkan ke Earth. Semua screen/shield di-ground ke Grounding Grid tersebut.

Working Effectively and Safely in an Electrical Environment

When the electrical team arrives on site to, let us say,
‘first fix’ a new domestic dwelling house, the downstairs
floorboards and the ceiling plasterboards will
probably not be in place, and the person putting in
the power cables for the downstairs sockets will need
to step over the floor joists, or walk and kneel on
planks temporarily laid over the floor joists.
The electrical team spend a lot of time on their hands
and knees in confined spaces, on ladders, scaffold
towers and on temporary safety systems during the
‘first fix’ of the process and, as a consequence, slips,
trips and falls do occur.
To make all working environments safer, laws and

safety regulations have been introduced. To make yourworking environment safe for yourself and those
around you, you must obey all the safety regulations
that are relevant to your work.
The many laws and regulations controlling the working
environment have one common purpose, to make
the working environment safe for everyone.
Let us now look at some of these laws and regulations
as they apply to the Electrotechnical Industry.

Statutory Laws
Acts of Parliament are made up of Statutes. Statutory
Laws and Regulations have been passed by Parliament
and have therefore become laws. The City and Guilds
Syllabus requires that we look at seven Statutory
Regulations.
1. The Health & Safety at Work Act 1974
◆ The purpose of the HSAWA is to provide the legal
framework for stimulating and encouraging high
standards of health and safety at work.
◆ The Act places the responsibility for safety at
work on both workers and employers.
◆ The HSAWA is an “Enabling Act” which allows the
Secretary of State to make further regulations
and modify existing regulations to create a safe
working environment without the need to pass
another Act of Parliament.

2. Electricity at Work Regulations 1989
◆ These Regulations are made under the Health &
Safety at Work Act and are enforced by the
Health & Safety Executive (HSE).
◆ The purpose of the Regulations is to “require
precautions to be taken against the risk of death or
personal injury from electricity in work activities”.
◆ An electrical installation wired in accordance
with the IEE Regulations BS 7671 will also meet
the requirements of the EWR.
3. The Electricity Safety, Quality and
Continuity Regulations 2002
◆ These Regulations are designed to ensure a
proper and safe supply of electrical energy up to
the consumer’s mains electrical intake position.
◆ They will not normally concern the electrical
contractor, except in that it is these Regulations
which set out the earthing requirements of the
supply.
4. The Management of Health & Safety at
Work Regulations 1999
◆ To comply with the Health & Safety at Work Act
1974 employers must have “robust health and
safety systems and procedures in the workplace”.
◆ Employers must “systematically examine
the workplace, the work activity and the
management of safety through a process of
risk assessment”.

◆ Information based upon the risk assessment
findings must be communicated to relevant staff.
◆ So, risk assessment must form a part of any
employer’s “robust policy of health and safety”.
5. Provision and Use of Work Equipment
Regulations 1998
◆ These Regulations place a general duty of care
upon employers to ensure minimum requirements
of plant and equipment used in work activities.
◆ If an employer has purchased good quality plant
and equipment, and that plant and equipment is
well maintained, there is little else to do.
6. COSHH Regulations (2002)
◆ The Control of Substances Hazardous to Health
Regulations (COSHH) control people’s exposure
to hazardous substances in the workplace.
◆ Employers must carry out risk assessments
and, where necessary, provide PPE (Personal
Protective Equipment) so that employees will
not endanger themselves.
◆ Employees must also receive information and
training in the safe storage, disposal and
emergency procedures which are to be followed
by anyone using hazardous substances.
7. Personal Protective Equipment Regulations (PPE)
◆ PPE is defined as all equipment designed to be
worn or held in order to protect against a risk to
health and safety.

◆ This includes most types of protective clothing
and equipment such as eye, foot and head
protection, safety harnesses, life jackets and
high visibility clothing.
◆ Employers must provide PPE free of charge and
employees must make use of it for their
protection.
◆ Figure 1.1 below shows the type of safety signs
which might be used to indicate the type of PPE
to be worn in particular circumstances for your
protection.
Working Effectively and Safely in an Electrical Environment 7
Have