Term
| Describe how power supplies are applied to electronics. |
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Definition
| Change available electrical energy to the form required by the circuits of the system. |
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Term
| What are some power supply maintenance activities and systems that have shock hazards? |
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Definition
-Using M&TE
-Bench testing
-Removal/Installation on energized systems.
-ALL electronic systems have shock hazards. |
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Term
| What are the termination points on a power supply used for? |
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Definition
-Ground
-Input - normally AC
-Output "+" and "-" - terminals connect the power supply to the load
-Sens + and - or sensing - Used for regulation and can be LOCAL or REMOTE. Used to minimize the effect of the output leads. |
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Term
| Some power supplies offer several design options. What are they? |
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Definition
-D.C. Input - needed if the SUPPLY VOLTAGE is DC.(Ex: Sequencers and 7300)
-Alarm - terminals connect supply auxiliary relay contacts to an alarm system to communmicate power suplly failure.
-Power On Reset - is a pulse from the supply to the sytem and occurs when supply ouput is restored.
-Interlock - shuts down the supply when a circuit board is removed. After the board is reinstalled, a reset button is depressed to restore supply output.
-A.C. Output - provides AC output. |
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Term
| How do you connect M&TE to a power supply? |
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Definition
-Vendor manual will describe requirements.
-NEVER use a decade box as a load.
-Output voltage is measured in parallel across load. |
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Term
| What are the functions of available power supply adjustments? |
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Definition
-Voltage adjust - sets the desired output voltage. Can be local or remote.
-Current limit adjust - sets the point where current stops increasing by dropping output voltage. Makes power supply short circuit proof.(protects power supply)
Overvoltage protection adjust - sets the point where the supply will crowbar the ouput to zero.(Protects load) |
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Term
| How do you restore supply output after an over-voltage condition? |
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Definition
| Momentarily inerrupt supply input line voltage. |
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Term
| How are converters used in process control applications? |
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Definition
-Provide an INTERFACE and/or ISOLATION between instruments that have incompatible signals.
-Protects upstream devices from downstream failures. |
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Term
| How is M&TE connected to test/calibrate current and voltage converters? |
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Definition
-Preferred method is to read the voltage across a series resistor.
-Usually requires 2 DVMs. One at input and output with signal source. |
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Term
| What are the two major components of current and voltage converters? |
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Definition
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Term
| Explain the operation of current and voltage converters. |
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Definition
-The transmitted current(I) develops a voltage across resistor Ra that is proportional to the input current.
-This voltage is biased by the zero pot to take out the zero suppression.
This voltage is then sent to the op amp to produce a 0-10 VDC output. |
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Term
| Calculate converter input/output values based on converter application. |
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Definition
4-20 mA = 0-10 VDC
10V/16mA - .625V/mA
Eout = (Iin x .625V/mA - 4 mA) |
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Term
| What adjustments need to be made to calibrate a current or voltage converter? |
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Definition
-Zero and span.
-Normally fail with a zero output. |
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Term
| Name and describe the types of position transmitters. |
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Definition
-Resolvers and Synchros - resolver has 2 stator windings 90 degrees apart and a synchro has 3 stator windings 120 degrees apart.
-Inductive Plates - essentially a resolver whose windings have been projected onto a linear medium.
-Pulse Position - use a grating and a photocell to produce pulses to an up/down counter to track position.
-Magnetic Pin or Tooth - used when position accuracy down to 0.00005 in. is req'd.
-Rotary Encoders - absolute and incremental provide output signals representative of shaft gearing rotation.
-LVDTs - magnetic iron core, moves axially within a cylindar which changes the voltages being induced in the secondary windings. (At 50% valve postion = 0 Vdc)
-Proximity Probe |
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Term
| What are the major components of a position transmitter? |
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Definition
| -Primary winding, opposing secondary windings and a moveable core. |
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Term
| How are position transmitters used in the field? |
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Definition
-LVDTs-Case expansion on main turbine, throttle and governor valve actuator servo system feedback and modulating target rock valve acutator feedback. Output is converted to a +/-DC voltage with 50% valve position output typically at 0 VDC.
-Resolvers & Synchros-Shafts, gears and robot arms.
-Pulse Position Transmitters-Computer printers
-Potentiometers-Recorders, Viper Flow Scanner and MS/PORV Actuator
-Rotary Encoders-Absolute Encoders are used in the INCORE Drive Units. |
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Term
| How do you connect M&TE and calibrate postion transmitters? |
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Definition
-Calibrated by positioning the shaft, table, arm, etc. to a zero reference position and then mechanically adjusting the position transmitter until its readout indicates zero.
-A resolver can also be zeroed by locking the gears in a zero reference position, connecting a DVM on volts AC function to the S1-S3 winding, and then turning the resolver case until the DVM reads 0 VAC. |
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Term
| How do you connect M&TE and calibrate postion transmitters? (cont'd.) |
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Definition
-LVDT calibration is determined by the system, the work control document and scaling.
-The S/G PORV Actuators use a cylindrical dual element potentiometer as a position transmitter.
One element is for position feedback to the servo amp. The other is used to develop indication.
-The potentiometer pickup arm is mechanically adjusted to match calve stroke length. |
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Term
| List five functions that electronic controllers perform. |
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Definition
-Location
-Signal Isolation
-Signal Conversion
-Signal Comparison
-Process Indication |
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Term
| What are the functions of various controller adjustments? |
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Definition
-Gain Control Adjustment Knob - varies feedback voltage to gain amplifier.
-Integral/Reset Rate Adjustment Knob - Sets integral time, normally 5-200 sec.
-Derivative/Rate Adjusment Knob - Determines controller initial rate of response to a process change. |
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Term
| Label the component parts of an electronic controller. |
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Definition
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Term
| What are the advantages of a digital controller? |
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Definition
-No potentiometers to adjust(drift does not occur).
-Digital display is more readable.
-No indicator needles to stick.
-Utilize contact outputs for alarms to be generated w/o use of instrumentation.
-Online diagnostics to monitor controller and loop health.
-Have MODBUS addressing to allow control of several controllers from one location.
-PB, Reset and rate are automatically adjusted.(Self-tuning) |
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Term
| What are some disadvantages of a digital controller? |
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Definition
-D/A or A/D causes step changes due to their conversion method that can result in cycling the final control element.
-Loss of indicating display
-Affected by RFI(Radio frequency). |
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Term
| How does the primary and secondary loop interact in a cascade control system? |
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Definition
-More than one control loop in Cascade.
-Primary(Master) loop regulates a controlled variable that is to be kept at a constant value and the second loop adjusts a second controlled variable that can cause fluctuations in the first controlled vaiable. |
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Term
| What are some advantages of cascade control? |
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Definition
-Reduced disturbance effects.
-More precise automatic adjustment.
-Uses standard instrumentation.
-Minimal cost. |
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Term
| What is a major characteristic of feedfoward control? |
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Definition
| -Controlled variable is not used in determining the appropriate value for the manipulated variable. |
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Term
| What is the purpose of using feedback trim in a feedforward control system? |
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Definition
-A problem with feed forward control is the change in parameters that affect the controlled variable and are not included in the energy balance equation.
-Feedback trim corrects heat and energy loss.
-Additional component for feedback trim is a temperature controller. |
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Term
| What are two methods to compensate a digital controller and minimize its disadvantages? |
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Definition
-Controllers are designed with diagnostic software to monitor controller's performance.
-Fault tolerate control scheme. |
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Term
| What precautions must be taken when working on controller that have a daisy chaned wiring scheme? |
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Definition
| -Evaluate the effect on system and instrument prior to lifting leads. This type of wiring configuration is normally found on AC or DC supply voltages. |
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Term
| Explain the operation of a programmable recorder. |
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Definition
-Handle a wide variety of inputs; including VDC, T/C, RTD and current.
-Can be calibrated using menu driven sequence via keyboard, operator display and vendor manual. |
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Term
| What is the programming sequence to install point parameters and personalized features? |
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Definition
-Programming is required to establish range and span data, define functions, and personalize features.
-Manuals provide a HOW TO flowchart and parameters are stored in EEPROM or non-volatile memory. |
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Term
| What are the steps to calibrate a programmable recorder. |
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Definition
-Vendor manual and a presicion voltage source is req'd for most calibrations.
-ZERO and SPAN may or may not be used. |
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Term
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Definition
-Initiated printouts.
-3 categories: Normal Operation, System and Program. |
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Term
| What are some troubleshooting techniques specific to programmable recorders? |
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Definition
-Error message display
-Diagnostic test can be run when power is turned on or through the menu. |
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Term
| Explain the design, construction and operation of a non-programmable recorder. |
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Definition
-Zero and Span pots
-Analog input, print drive and chart drive. |
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Term
| Describe how to calibrate a non-programmable recorder. |
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Definition
| -Apply input value, compare with output. Calibrate per vendor manual. |
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Term
| What are the hazards associated with analytical instruments? |
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Definition
| -Chemical exposure, temp, pressure, radiological, reagents. |
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Term
| Name the types of analyzers at STP. |
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Definition
-In-line or bench top.
-Hydrogen, Chlorine, Hydrazine, Gas Chromatographs, Boron, Moisture, Sodium, Silica, Hardness, Oxygen, Conductivity, pH and ORP. |
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Term
| How does an analytical instrument work? |
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Definition
| -Observes the consequences of interation between a substance and an external source of energy. |
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Term
| How does a pH analyzer work? |
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Definition
-Determines the concentration of hydrogen ions
-An EMF is developed across the glass barrier proportional to the difference in hydrogen ion concentration of the unknown solution to the known KCl solution. |
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Term
| Define the values on the pH sclae. |
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Definition
0-7 - Acid
7 - Neutral
7-14 - Base, Alkaline or Caustic |
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Term
| How does a conductivity analyzer operate? |
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Definition
-Uses two parallel platinum electrode plates immersed in a solution.
-Uses a known voltage and current from EMF to determine the resistance between electrodes. Ohm's Law |
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Term
| What is the proper way treat analytical sensors? |
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Definition
-Soft cloth and tap water.
-Electrodes must remain in a solution to prevent drying out.
-DO NOT use brushes to avoid scaching electrode surfaces. |
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Term
| Outline the sequence req'd to program a microprocessor based analytical instrument. |
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Definition
| -Set DIP switches, program time, alarms, etc and calibrate using vendor manual and scaling document. |
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Term
| How do you calibrate a pH analyzer? |
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Definition
-Standardizing
-Two known buffer solutions are used and analyzer is adjusted per scaling. |
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Term
| How do you calibrate a conductivity analyzer? |
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Definition
-Replace the probe with a decade box and the temperature compensator with a resistor value specified by the vendor manual.
-Adjust as necessary. |
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