Detections Sensor

JENIS - JENIS DETEKTOR    
Secara umum detektor dibagi menjadi 2 jenis :

• Deteksi dengan kontak langsung (bersentuhan dengan benda benda yang akan dideteksi)
• Deteksi dengan tidak kontak langsung (tidak bersentuhan dengan benda yang akan dideteksi)

Detektor yang termasuk dalam jenis DETEKSI DENGAN KONTAK LANGSUNG :

1. Limit Switch
2. Pressure Switch

Detektor yang termasuk dalam jenis DETEKSI DENGAN TIDAK KONTAK LANGSUNG :

1. Photoelectric
2. Proximity
3. Ultrasonic

Limit Switch
Bekerja berdasarkan perubahan posisi dari actuator (Bagian yang bersentuhan dengan objek yang dideteksi) yang menggerakkan kontak blok yang berada di dalam limit switch tersebut.
Pemilihan dari jenis actuator ini disesuaikan dengan aplikasi, ukuran, jenis dan bentuk obyek yang akan dideteksi.
Pressure Switch
Adalah alat untuk mempertahankan tekanan pada batasan tertentu (diantara batas PH, dengan batas bawah PB). Apabila tekanan mencapai nilai PH (maka switch akan berubah kondisi dari On ke Off) dan apabila tekanan berkurang dan mencapai nilai PB (maka switch akan berubah kondisi dari Off ke On).
Selisih antara nilai PH dan PB disebut Differensial.

Ada 2 tipe Pressure Switch: Fixed Differential dan Adjustable Differential

1. Diferensial tetap (Fixed differential): Nilai diferensial tetap (tertentu), hanya nilai PH yang dapat diatur. Nilai PB didapat dari nilai PH dikurangi dengan nilai diferensialnya.
2. Diferensial tidak tetap (Adjustable differential): Nilai diferensialnya dapat diatur, karena baik nilai PH maupun PB nya masing-masing dapat diatur.

Pressure Switch dibagi menjadi 2 jenis: Elektromekanik dan Elektronik    

1. Elektromekanik: Bekerja dengan menggunakan komponen mekanik seperti pegas untuk mengukur tekanannya.
2. Elektronik: Bekerja dengan menggunakan komponen elektronik (lebih presisi).

Pressure Transmitter atau Pressure Sensor alat pengukur tekanan dengan output berupa output analog (dapat berupa tegangan 0-10VDC atau berupa arus 4..20 mA), perubahan nilai output tersebut sebanding dengan perubahan tekanan yang dirasakan.

Proximity   

Ada dua tipe proximity: Inductive Proximity dan Capacitive Proximity.

- Inductive Proximity:

• 
  
  Bekerja berdasarkan perubahan induktansi apabila ada obyek metal yang berada dalam daerah kerjanya. Hanya dapat mendeteksi benda yang terbuat dari metal, dengan jarak deteksi maksimum 6cm. Jarak deteksi dipengaruhi dari jenis metal obyeknya (misal: jarak deteksi untuk besi berbeda dengan tembaga, dll).
  
  

- Capacitive Proximity:

• 
  
  Bekerja berdasarkan perubahan kapasitas apabila ada obyek yang berada dalam daerah deteksinya.
  
  
• 
  
  Dapat mendeteksi semua jenis benda dalam jarak deteksi maksimum 2 cm.
  
  
• 
  
  Berdasarkan tipe pemasangan / mounting-nya, proximity ada 2 macam: Flush dan Non Flush.
  
  
• 
  
  Flush maksudnya dalam pemasangannya dapat dibenamkan dalam metal.
  
  
• 
  
  Non Flush maksudnya dalam pemasangannya harus diberi jarak antara proximity dengan benda-benda metal disekitarnya.
  
  

Ultrasonic
Bekerja dengan mendeteksi pantulan gelombang suara ultra oleh obyek yang berada dalam daerah deteksinya.
Dapat mendeteksi segala jenis benda dalam jarak deteksi maksimum 1 M.

Photoelectric   

• Terdiri dari bagian transmitter (pemancar cahaya) dan bagian receiver (penerima cahaya).
• Photoelectric bekerja berdasarkan ada tidaknya cahaya (berasal dari transmitter) yang diterima oleh bagian reciever.
• Ada dua jenis switching dari sensor ini, yaitu Dark On dan Light On.

- Dark On: Sensor akan On jika tidak ada cahaya yang diterima oleh receiver.
- Light On: Sensor akan On jika ada cahaya yang diterima oleh receiver.    

Photoelectric dapat mendeteksi segala jenis benda dengan jarak deteksi maksimum 100 M.
Sistem kerja photoelectric dibagi menjadi lima, yaitu: Thru-beam, Reflex, Polarized Reflex, Diffuse dan Diffuse with Background Suppression.

• Thru-beam: Pada tipe ini Transmitter dan Receiver terpisah dalam 2 unit, bila obyek menghalangi cahaya dari transmitter ke receiver maka keluaran dari sensor ini akan berubah sesuai dengan jenis switching dari sensor tersebut.
• Reflex: Pada tipe ini Transmitter dan Receiver berada dalam 1 unit, dan dibutuhkan sebuah reflektor untuk memantulkan cahaya dari transmitter ke receivernya. Bila obyek menghalangi cahaya yang diterima receiver, maka keluaran dari sensor akan berubah sesuai dengan jenis switching-nya. Tipe ini tidak bisa digunakan untuk mendeteksi obyek yang mengkilap, karena pantulan cahaya dari trans mitter oleh obyek yg mengkilap dapat mengacaukan kerja sensor tersebut.
• Polarized Reflex: Merupakan pengembangan dari tipe refleks, sehingga tipe ini bisa digunakan untuk mendeteksi obyek yang mengkilap.
• Diffuse: Pada tipe ini Transmitter dan Receiver berada dalam 1 unit. Apabila receiver menerima cahaya dari transmitter yang dipantulkan oleh obyek, maka keluaran dari sensor akan berubah sesuai dengan jenis switching-nya .
• Diffuse With Background Suppression: Tipe ini merupakan pengembangan dari tipe diffuse, sensor ini dapat digunakan untuk mendeteksi obyek dengan latar belakang. Jarak deteksi pada sistem ini dapat diatur sehingga hanya pantulan dari obyeknya yang mengubah keluaran dari sensor, sedangkan pantulan dari latar belakang tidak akan mengubah keluaran dari sensor.

Osiconcept (Offering Simplicity through Innovation) merupakan konsep baru dari Schneider Electric di bidang Sensor (Photoelectric, Proximity, Limit Switch, Pressure Switch). Dengan konsep ini memudahkan Anda dalam memilih sensor yang tepat sesuai dengan kebutuhan aplikasi Anda:

1. Photoelectric dengan Osiconcept menggabungkan ke 5 tipe (thru-beam, reflex, polarized reflex, diffuse dan diffuse with background suppression) include productnya.
2. Proximity dengan Osiconsept menggabungkan tipe Flush dan Non Flush , include product.
3. Limit Switch dengan Osiconcept menawarkan limit switch modular yaitu: baik kepala, body, dan kontak blok dapat saling dipertukarkan, sehingga menghemat waktu dan biaya pemeliharaan
4. Pressure Switch dengan Osiconcept menawarkan kemudahan dalam hal pengaturan parameter tekanan (PH, PB, dll.)

Keuntungan dengan Osiconcept:

• Bagi pembuat mesin / OEM: Membuat desain mesin menjadi lebih mudah; dengan Osiconcept sensor dapat diadaptasikan dengan berbagai keadaan / kondisi sesuai dengan keinginan Anda. Osiconcept membuat mesin Anda lebih fleksibel untuk berbagai aplikasi.
• Bagi Penjual / Toko: Memudahkan Anda dalam memilih sensor yang cocok dengan kebutuhan pelanggan; Osiconcept menggabungkan beberapa jenis sensor ke dalam satu produk sehingga mengurangi jumlah pilihan sensor. Sensor dengan Osiconcept fleksibel untuk berbagai aplikasi pelanggan Anda.
• Bagi Pengguna / end user: Mempersingkat waktu berhenti mesin Anda pada waktu pemeliharaan; Osiconcept menawarkan produk sensor yang fleksibel, mudah dalam instalasi dan pengaturannya.

Schneider Electric dengan product Telemecanique menyediakan 3 pilihan untuk sensor:

• Tipe Universal: Dilengkapi dengan Osiconcept, cocok untuk berbagai kebutuhan Anda.
• Tipe Optimum: Sensor tipe ekonomis dengan berbagai pilihan jenis yang dapat disesuaikan dengan kebutuhan Anda.
• Tipe Aplikasi: Untuk aplikasi khusus yang membutuhkan sensor dengan spesifikasi tertentu.

Tipe koneksi:

• Kabel: sensor telah dilengkapi dengan kabel, sehingga cocok untuk pemasangan di daerah lembab (IP lebih tinggi).
• Konektor: sensor dilengkapi dengan konektor, memudahkan dalam pemeliharaan (penggantian).
• Screw clamp terminals: cocok apabila sensor dipasang cukup jauh dari interfacenya (PLC, Pilot Light dll.) dan dibutuhkan panjang kabel yang fleksibel.

HVAC FORMULA

Useful Formulas

 
-        Total Heat (BTU/hr) = 4.5 x cfm x  ∆h (std. air)
-        Sensible Heat (BTU/hr) = 1.1 x cfm x  ∆t   (std. air) -        Latent Heat (BTU/hr) = 0.69 x cfm x ∆gr. (std. air)
    NOTE: For conditions other than standard air please see this page.

-        Total Heat (BTU/hr) = 500 x gpm x  ∆t (water)

-        TONS = 24 x gpm x ∆t (water)

-        GPM cooler = (24 x TONS) / ∆t (water)

   

-        Fluid Mixture   T_m = (Xt₁ + Yt₂) / X + Y     (this works for air or water)

-        BTU/hr = 3.413 x watts = HP x 2546 = Kg Cal x 3.97

-        Lb. = 453.6 grams = 7000 grains

-        psi = ft. water/2.31 = in. hg/2.03 = in. water/27.7 = 0.145 x kPa

-        Ton = 12,000 BTU/hr = 0.2843 x KW

-        HP (air) = cfm x   ∆p (in.H₂O)/6350 x Eff.

-        HP (water) = gpm x  ∆p (ft.)/3960 x Eff.

-        Gal. = FT³/7.48 = 3.785 Liters = 8.33 lb. (water) = 231 in. ³

-        gpm = 15.85 x L/S                                                                         

-        cfm = 2.119 x L/S                                          

-        Liter  = 3.785 x  gal = 0.946 x quart = 28.32 x ft³

-        Therm = 100,000 BTU = MJ/105.5

-        Watt/sq. ft. = 0.0926 x W/M²

-        yd. = 1.094 x M

-        ft. = 3.281 x M

-        ft² = 10.76 x M²

-        ft³ = 35.31 x M³

-        ft/min = 196.9 x M/S

-        PPM (by mass) = mg/kg

NOTE:         Liter/sec is the proper SI term for liquid flow.  M³/sec is the proper SI term for airflow. Due to the awkward nature of using M³/S at low air flow rates (lots of decimal points), L/S is commonly used to express air flow for HVAC applications.

HVAC FORMULAS

Dewpoint and Wetbulb Temperature

The following equations are used to calculate the wetbulb temperature of air given the drybulb temperature and relative humidity %. The equation assumes that the ambient barometric pressure is constant at a value of 29.15 "Hg since the change in wetbulb temperature is very insignificant with changes in the ambient barometric pressure.

Input Variables		System Variables		Output Variables
RH	Relative Humidity %	e	Ambient vapor pressure in kPa	Td	Dewpoint temperature in degrees C
T	Drybulb temperature in degrees C	GAMMA	Constant based upon ambient barometric pressure	Tw	Wetbulb temperature
		DELTA	Constant
Equations
e	(RH / 100) * 0.611*EXP(17.27*T/(T+237.3))
Td	[116.9 + 237.3 ln(e)] / [16.78 – ln(e)]
GAMMA	0.00066*P (Use P = 98.642 kPa. This is equal to 29.15 "Hg… about the pressure we normally experience.)
DELTA	4098*(e / Td + 237.3)^2
Wetbulb Temperature in Degrees F Equals:
Tw	1.8 * [[(GAMMA*T) + (DELTA*Td)] / (GAMMA + DELTA)] + 32
Dewpoint Temperature in Degrees F Equals:
Td	1.8 * [[116.9 + 237.3 ln(e)] / [16.78 – ln(e)]] + 32

Air Handling Unit Tonnage Output

The following equation calculates the refrigeration output in Tonns of a coil.

Input Variables		Output Variables
T1	Entering air temperature of the coil in degrees F	TONNS	Dewpoint temperature in degrees F
T2	Leaving air temperature of the coil in degrees F
CFM	Volume of air passing through the coil
Equation
TONNS	1.08*(T1 – T2)*CFM

Chiller Tonnage Output

The following equation calculates the refrigeration output in Tonns of a chiller.

Input Variables		Output Variables
T1	Chilled water return temperature in degrees F	TONNS	Energy output of the chiller
T2	Chilled water supply temperature in degrees F
GPM	Volume of water passing through the chiller
Equation
TONNS	GPM*(T1 – T2) / 24

Chiller Coefficient of Performance

The following equation calculates the ratio of energy used to the energy output of a chiller.

Input Variables
T1	Chilled water return temperature in degrees F
T2	Chilled water supply temperature in degrees F
GPM	Volume of water passing through the chiller
KW	Kilowatts

Output Variables
COP	Energy output of the chiller

Equation
COP	(T1 – T2) * GPM * 0.0417 / (0.28433 * KW)

VAV Box Air Flow Rate (CFM)

Input Variables
A	Duct area in sq. ft
Pv	Pressure in inches of H2O from PV3

Output Variables
V	Velocity of the air
CFM	Cubic feet of air per minute

Equation
Q	AV
0.0763 is the density of dry air at 60o F The duct diameter units are in ft.
CFM	1096(Duct Diameter/2)2(√(Pv/.0763))

Heat Index Calculation

The following equation calculates the heat index of the outside air.

Input Variables
Tf	Outside air temperature in degrees F
RH	Outside air relative humidity % (enter 50 for 50%, etc.)

Output Variables
HI	Heat index

Equation

HI

HI = -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR - 6.83783x10-3T2 - 5.481717x10-2R2 + 1.22874x10-3T2R + 8.5282x10-4TR2 - 1.99x10-6T2R2 where T = ambient dry bulb temperature (°F) R = relative humidity (integer percentage). Because this equation is obtained by multiple regression analysis, the heat index value (HI) has an error of ±1.3°F. Even though temperature and relative humidity are the only two variables in the equation, all the variables on the lists above are implied.

Wind Chill Temperature Calculation

The following equation calculates the wind chill temperature of the outside air.

Input Variables
V	Outside air velocity in Miles per Hour
T	Outside air temperature in degrees F

Output Variables
WC	Wind chill temperature

Equation
WC	0.0817(3.71(V)^0.5 + 5.81 - 0.25V)(T - 91.4) + 91.4

Pressure Measurement

Velocity Pressure
Where V = Air Velocity (FPM) Pv = Velocity Pressure (in. w.g.)

Equivalent Measures of Pressure
1lb. per square inch	= 144lbs. per sq. ft. = 2.036in. Mercury at 32°F = 2.311ft. Water at 70°F = 27.74in. Water at 70°F
1 inch Water at 70°F	= .03609lb. per sq. in. = .5774oz. per sq. in. = 5774oz. per sq. in. = 5.196lbs. per sq. ft.
1 ounce per sq. in.	= 1272in. Mercury at 32°F = 1.733in. Water at 70°F
1ft. Water at 70°F	= .433lbs. per sq. in. = 62.31lbs. sq. ft.
1 Atmosphere	= 14.696lbs. per sq. in. = 2116.3lbs. per sq. ft. = 33.96ft. Water at 70°F = 29.92in. Mercury at 32°F
1in. Mercury at 32°F	= .491lbs. per sq. in. = 7.86oz. per sq. in. = 1.136ft. Water at 70°F = 13.63in. Water at 70°F

Compression Ratio
Compression Ratio	= Absolute Discharge Pressure / Absolute Suction Pressure
Absolute Discharge Pressure	= gauge reading + 15psi
Absolute Suction Pressure	= gauge reading + 15psi

Refrigerant Mass Flow Rate
Mass Flow Rate (Pounds/Minute)	= Piston Displacement X Refrigerant Density = (Cubic Feet/Minute) X (Pounds/Cubic Feet)

Plan for Sour Water

 Recycling Sour Water Stripper Bottoms for Cooling Towers, Boiler Feedwater

Oil refining is dependent on the use of the distillation process. However, in the course of this procedure, condensed water accumulates in the overheads of the extraction columns. While this water is essentially distilled, the soluble gases and soluble hydrocarbons remain entrained and are in equilibrium with ionic species in the water, depending on the pH.

In most refineries, the overheads send water to a central collection where it is stream-stripped for bulk removal of NH3 and H2S. There are other similar small-volume sources of water that are sent to the sour water stripper (SWS) as well. In medium-sized refineries, there are typically 30 sources feeding the stripper. Some of the SWS-treated water, or "Bottoms," is sent to the desalter as wash water and from there becomes wastewater. The excess of unused SWS Bottoms for desalting is transferred directly to the wastewater treatment plant (WWTP).

With appropriate treatment of the SWS Bottoms -- to the extent where NH3, H2S, short-chain light hydrocarbons, and amines are decreased to acceptable levels -- the value of the water increases and cannot be wasted on the lower-quality needs of desalter wash water. Under normal and proper operating conditions, the SWS water has no significant levels of calcium, magnesium or iron -- the primary scale-forming inorganic contaminants of concern in

After specific treatment of the SWS Bottoms for these contaminants, this water is not only considered a suitable quality for steam and cooling systems but actually becomes a superior quality similar to steam condensate. Further, this captured SWS-treated water produces substantial fuel value in the form of heat. Similar to steam condensate, this water can bypass normal boiler feedwater pretreatment systems such as ion exchange or reverse osmosis (RO) and can proceed directly to the boiler deaerator.

Occasionally, SWS units are not operated or maintained correctly. A system with a significant presence of the three aforementioned inorganic cations would be overlooked as a candidate for water reuse. Most commonly, these cations enter the SWS system either by cooling water intrusion from piping and condenser leaks or by using an unsuitable water injection source in the distillation column overheads for the forcing of the dewpoint to initiate condensation.

These two conditions ultimately cause major problems in the SWS units themselves, such as the deterioration of the SWS trays, which will cause serious SWS performance problems and will require repairs. These problems almost always are short term with respect to the presence of these inorganic cations in the Bottoms, as the SWS cannot operate very long under these conditions.

In addition to boiler feedwater supply, the same considerations regarding scale formation exist as the criteria for the justification of SWS water reuse as cooling tower supply water; this also has an attractive return on investment. The validation for this cooling tower make-up can be found in the increased cycles of concentration, which would be tolerable in the cooling towers with the treated SWS water. This translates to substantial reductions in the volume of supply water used, wastewater generated and cost of chemical treatment in cooling tower operations.

The economic basis for the justification of water reuse investment at the SWS is substantially more attractive for boiler feedwater than it is for cooling tower make-up water. The return on investment for SWS Bottoms reuse as boiler feedwater is based on the reduction in the cost of treating wastewater; the decrease in the cost of supply water pretreatment; and the capture of SWS heat, which reduces deaerator heating fuel costs.

Interestingly, for those plants required to meet selenium NPDES permit limits, the routing of the SWS Bottoms to the boilers inherently extracts more than 80 to 90 percent of the total selenium load to the wastewater treatment plant, thus eliminating any selenium removal needs in the facility in almost all cases.

HVAC FORMULA

Cooling Coil Calculations Actual Air vs. Standard Air CFM

   

The question begins this way: 

"The performance of your unit is not correct."

Why?

"Because when I calculate the coil load from the stated conditions I do not get the capacity shown"

   

Answer:

When calculating the Total Capacity do not use Qt = 4.5 * cfm * (h₁ – h₂)

Because 4.5 is derived for standard air as follows:
ma = cfm * Density * 60 where the density of standard air = .075 lba/ft³

At 100 DB and 78 WB, the W = .015601 lbw/lba

h = ha + Whg = cpa*T + W*(1061 + .444*T) Btu/lba

h₁ =.24*100 + .015601*(1061 + .444*100) = 41.25 Btu/lba

At 57.50 DB and 57.30 WB, the W = .0099622 lbw/lba

h₂ = .24*57.50 + .0099622*(1061 + .444*57.50) = 24.62 Btu/lba

If you use this equation then you will get the following:

Qt = 4.5 * 15000 * (41.25 – 24.62) = 1,122,525 Btu/hr, or a perceived error of 8.3

Coil programs use actual conditions:

At 100 DB and 78 WB, the W = .015601 lbw/lba, Density = .06914 ft³/lba

 h₁ = 41.25 Btu/lba from above

 At 57.50 DB and 57.30 WB, the W = .0099622 lbw/lba

 h₂= 24.62 Btu/lba above

 ma = CFM*Density*60 = 15000 * .06914 * 60 = 62,226 lba/hr

 Qt = ma * (h[1] – h[2]) = 62226*(41.25 – 24.62) = 1,034,818 Btu/hr

 
When calculating the sensible capacity do not use Qs = 1.1 CFM *(T₁-T₂):

 Because the 1.1 is derived from standard air as follows:

 m_{a *} C_pm = SCFM*Density_Std*(C_pa + W*C_pw)

 m_{a *} C_pm = SCFM *.075 * 60 * (.24 + .0093*.444) = 1.1*SCFM

 If you use this equation then you will get the following:

 Qs = 1.1 * 15000 * (100-57.50) = 701,250 Btu/hr                           

 Coil programs use actual conditions:

 At 100 DB and 78 WB, the W = .015601 lbw/lba, Density = .06914 ft³/lba

 At 57.50 DB and 57.30 WB, the W = .0099622 lbw/lba

 ma = CFM*Density*60 = 15000 * .06914 * 60 = 62226 lba/hr

 Cpm = (C_pa + W*C_pw)                  Btu/(lba – F)

 Qs = ma * Cpm * (T[1] – T[2])

 Qs = 622226*(.24+.015601*.444)*(100-57.5) = 652,988 Btu/hr

 The Total Latent Load is computed from:

 Q_L = Q_t – Q_s

 Using standard Air   Q_L = 1,034,818 - 701,250 = 333,568 Btu/hr

 Using actual air:  Q_L = 1,034,818 - 652,988 = 381,830 Btu/hr 

The above shows a sea level calculation.
The same equations apply for altitude however the true density must include DB, WB, and PB = altitude PB. PB altitude is calculated from the following equation:  PB = 14.696 * (1 - ALTITUDE*6.8753E-6)^5.2559

Overhead Electrical Power-Line Distribution

Methods of Feeding Overhead Electrical Power-Line Distribution Lines With BPL Signals and the Relationship of These Methods to the Radiated Emissions of the Conductors

1. Introduction 1.1 There are differences in the way that medium-voltage (MV)2 power-distribution lines conduct and radiate signals based on the way that RF power is fed to the lines. ARRL used a well-known antenna-modeling program, EZNEC PRO3 3.0 with the NEC-4.1 calculation engine4 to model a simple MV power line and two nearby amateur antennas, conservatively located 30 meters from the lines. A pictorial diagram of the model is shown in Figure 1. 1.2 Tables 1 and 2 show the results ARRL obtained by modeling three different ways of feeding the antenna: o Differential feed between two phases, at one end o One phase to earth ground, in the center o One phase fed differentially similar to the way a dipole antenna is fed, offset on the ungrounded phase

2. Description of the Model 2.1 The power-line radiator antenna model was configured with two 12.7 mm copper conductors5, 200 meters in length. They were placed 10 meters above ground. The ground was modeled with average conductivity and dielectric constant. The two conductors were parallel, spaced 1.0 meter. One of the conductors was grounded to simulate typical imbalance in the line. The ground connection consisted of four 10-meter radials, 5 cm above ground. This is a relatively poor RF ground, to simulate the typical poor RF characteristics of power-line grounds. (This also allows those that don’t have access to the NEC-4.1 software to duplicate the results using the more available NEC-2 calculation engine, which cannot handle direct ground connections the same way NEC-4.1 does.) 2.2 Differentially connected loads were placed at each end of the transmission line to properly model the signal losses from various loads present on the line (transformers, BPL modems). This power would not be radiated, so must be accounted for in the model. This also allows the software to calculate the relative efficiency of feeding the system at different points by comparing the power fed to the system and the power that reaches the load, simulating a BPL system modem or repeater. These loads are 50-j0 ohms. 2.3 Two amateur receive antennas are also included in the model. Antenna 1 is a half-wave dipole located 10 meters above ground, at the height of the power line, typical of many amateur tree-mounted antennas. This antenna is 30 meters distant from the line. Antenna 2 is a half-wave dipole located 30 meters above ground, 30 meters diagonally from the line.

The height of this antenna is representative of taller amateur tower installations. Each of these antennas has a 50-j0 ohm load in the center and EZNEC is used to calculate the power that reaches each load by radiation.

Figure 1: This is a pictorial of the model used by ARRL to calculate differences in the performance of BPL systems fed in different ways. Point 1 = Amateur half-wave dipole antenna, 10 meters high, 30 meters from line. Point 2 = Half-wave dipole antenna, 30 meters high, 30 meters diagonally from line. Point 6 = Single-phase differential “dipole” feed point. Points 7 and 8 = Two phase differential feed or load, as specified in Tables. Point 9 = Ground wire, fed where it connects to the phase. Point 10= Earth ground radials (4). 3. Results 3.1 The results of the modeling are shown in Tables 1 and 2.

Sekilas Industrial Process control & instrumentation

titipan dari forum sebelah

Halo temen2 fisika teknik, aq ingin sharing ttg dunia instrumentasi & sistem kendali industri proses (Industrial process control &i instrumentation), merangkum dari pengalaman temen2 alumni yg bekerja di dunia industri proses baik sebagai user, vendor DCS/PLC/SCADA dan kontraktor EPC..

sebagai basic mata kuliah pendukung, kuliah2 basic seperti mekanika fluida, thermodynamic, PPM, kontrol automatis,kontrol proses,dinamika system, sistem pengukuran, pemrograman, sistem digital dll sangat menunjang mempelajari instrumentasi industri

..

industri proses dikatagorikan sebagai industri yg mengolah bahan baku secara kontinyu dalam jumlah besar, seperti oil & gas company, chemical, power plant, fertilizer, petrochemical maupun cement.

sebuah plant proses (exmp: heat exchanger, pressurized vessel dll) dalam pengoperasiannya memerlukan instrumentasi untuk menunjang safety. tingkatan sistem instrumentasi dari yg awal sampai puncak:

1. BPCS (Basic Process Control System)

2. Alarm system

3. Safety Instrumented System (SIS), biasanya Emergency Shutdown System (ESD) & Fire Gas System (FGS)

4. Relief system (pengaplikasian Pressure Relief Valve/PRV)

Sebaiknya dibahas terlebih dulu sistem instrumentasi tingkatan yg pertama,yaitu BPCS.

sebuah loop sistem kendali proses memiliki element sensor, transmitter, controller,algoritma kendali,actuator & final element, serta plant proses/controlled variable (Basic Process Control System/BPCS).

A. Sensor

Variabel proses yg diukur dan dikontrol di industri proses adalah Flow, Pressure, Temp, Level, Analyzer, vibrasi, speed, weigh dll.

contoh:variabel proses yg penting adalah flow, pengukuran flow untuk liquid berbeda dengan fasa vapour,superheated steam & gas, karena liquid bersifat incompressible sehingga pengaruh temperature & pressure actual flowing fluida tidak berpengaruh pada densitas liquid (ingat prinsip thermodynamic).sebaliknya untuk gas, vapour & steam maka diperlukan kompensasi atas perubahan densitas akibat perubahan pressure & temperature flowing.

pengukuran flow ada 2 metode:mass flowrate (ada kompensasi densitas fluida terhadap perubahan Press dan Temp actual) & volume flowrate.

controh:

mass flowrate instrument adalah corriolis,multivariable flowmeter (punya Diff transm,Press transm & temp transm).

Volume flowrate adalah orifice,turbine meter,vortex dll.

kita ambil contoh sistem pengukuran Natural Gas metering (mass flowrate) untuk jual beli, seperti pada beberapa perushan gasl dll:

Intrument yg dipakai:

1.sensor flow yg dipakai adalah orifice (prinsip bernoulli), flow sebanding dengan akar beda tekanan.

2. Differential pressure transmitter, mengukur beda tekanan pada orifice dan menyampaikannya ke recorder/controller.

3.Pressure sensor (tipe diapragm sensor pada pressure transmitter), mengukur kompensasi perubahan densitas gas terhadap pressure.

4.Thermocouple, ngukur suhu actual gas flowing untuk kompensasi perubahan densitas gas terhadap temperatur.

5. Temperature transmitter (biasany electronic 4-20mA)

6. Pressure Control Valve, mengontrol pressure gas yg mengalir ke pembeli.

7. Pressure switch High/High High  (PSH/PSHH) dan pressure switch Low/ Low Low (PSL/PSLL),mendeteksi pressure gas.

   PSH terdeteksi=alarm,PSHH terdeteksi=operasi shutdown, PSL terdeteksi=Alarm, PSLL=operasi Shutdown

8. Shutt Down Valve (SDV), berfungsi sebagai actuator untuk memblock laju aliran gas ke pembeli apabila pressure aliran gas telah mencapai setingan PSLL atau PSHH (INTERLOCK ESD).

9. Gas analyzer,yaitu Gas Chromatograph (GC) untuk mengukur kadar komposisi berat jenis masing2 senyawa kimia dalam Natural Gas seperti metana,butana, Nitrogen dll.

10. Barton chart flow recorder

semua data2 dari sensor/transmitter tersebut dihitung oleh flow computation, dengan menggunakan rumus standard internasionalpengukuran, APPI (klo ga salah) yaitu AGA 3 gas flow calculation (aq ga hafal rumusnya hehe).tp satu hal yg jelas, teori2 thermodynamic & mekanika fluida berperan besar dalam perhitungan AGA 3.   

B.Transmitter

berfungsi mengirimkan sinyal elektric (4-20 mA) atau pneumatic (3-15 Psig) ke controller,proportional dengan nilai ouput sensor.

jenisnya: Pressure Transmitter, Differential Pressure Transm, Temp transm dll

C.Controller

alat pengendali bisa berupa electric/pneumatic controller yg tidak terdistribusi, maupun yg terdistribusi seperti DCS,PLC,SCADA (tuk remote/jarak jauh area)..saat ini PLC sudah memiliki fitur menyamai DCS (pny Human Machine Interface,analog I/O ribuan,PID control,data history & redundant controller),namun ada hal2 prinsip DCS yg tidak dimiliki oleh PLC yaitu (referensi dari vendor ABB):

1. Support Asset Management features

2. Support Safety System, ada istilah Safety Integrity level (SIL),panjang penjelasannya jadi silakan cari di internet saja hehe.

3. Integrated Development Software

untuk Plant yg menuntut safety tinggi, maka DCS lebih unggul daripada PLC, dgn adanya SIL 3 untuk DCS.untuk Pembangkit Listrik

Tenaga Nuklir (PLTN) maka memiliki SIL paling tinggi yaitu SIL 4.

D. Algoritma kendali

saat ini algoritma PID (Proportional Integral Derivative) masih umum digunakan, setahuku ada Model Predictive Control (MPC) yg mulai tersedia di salah satu vendor DCS. penggunaan MPC menandai babak baru sistem kendali proses, yaitu Advanced Process Control (APC) untuk optimasi sistem kendali.

PID control adalah Basic Regulatory Control System pada sebuah feedback control,namun di industri,sebuah proses plant memiliki banyak variable proses sehingga muncul istilah cascade, ratio, feedforward,three element,decoupler control (Advanced Regulatory Control) yg tetap menggunakan PID control sebagai basic algoritma.

E. Actuator & final element

biasanya adalah control valve, damper, motor (untuk speed & berat pada conveyor). yg populer di industri proses adalah control valve.

untuk regulatory (pengaturan) control:Pressure Control Valve (PCV), Flow Control Valve (FCV), Temp Control Valve (TCv), Level Control Valve (LCV), Hand Control Valve (HCV).

untuk On-Off control ; Motor Operated Valve (MOV), Remote Operated Valve (ROV).

untuk Emergency Shutt Down system (ESD): Shutt Down Valve (SDV),Blow Down valve (BDV).

penggunaan valve untuk regualtory, On-Off dan ESD masing2 memiliki karakteristik yg berbeda.

F. Plant proses

plant proses adalah tempat dimana berlangsungnya suatu proses, contoh sebuah tangki yg didalamny bisa terdapat beberapa feedback control seperti Level Control System, Pressure Control System maupun Flow Control System dan terdapat cascade, ratio,decoupler control.penguasaan terhadap proses2 fisika pada suatu plant, dari pengalaman,seharusnya intrument & process control engineer harus bisa sehingga bisa menjabarkan dinamika system pada suatu plant. ada hubungannya nanti dengan proses penentuan nilai variabel2 Tuning PID (Proportional band, reset time(I) dan derivative time) dari orde proses yg dihadapi maupun penentuan jenis regulatory apa yg cocok dgn proses entah itu cascade, ratio, feedforward dll.