REGIONAL METROLOGY CONFERENCE 2010

ELECTRICAL

INSTRUMENTATION

By: A. Ochieng

08. 10. 2008

INSTRUMENTATION

1. INTRODUCTION

DEFINITION:

Instrumentation is the branch of science that deals with measurement and control.

It is a specialization focused on the principle and operation of measuring instruments which are used in design and configuration of automated systems.

2 Instrument Composition

An instrument consists of;

– system under measurement or measurand, – sensors/transducers, – signal conditioners, – signal processors and– effectuator / output (display, recording or

storage).

– 2.1 These measured values include:– pressure - flow – temperature - level – position, speed, vibration or acceleration)– density - viscosity – radiation - current – voltage– inductance - capacitance – frequency - resistance – chemical composition

The can be an output in the form of:

-analogue or digital readout,

-graphical display

-or video display.

2.5 Control

examples :

Device Field Parameters

Valve Flow, Pressure

Relay Voltage, Current

Solenoid Physical Location, Level

Circuit breaker Voltage, Current

3.0 INSTRUMENT OPERATION

Instruments mode of operation may be either

-manual,

-semi-automatic or

-automatic

This depends on the purpose and technology at the time of manufacture

4.0 Instrument Failure

Failures may be categorised as:-

- intermittent or permanent,

- partial or complete,

- sudden or gradual,

- Catastrophic or degrading.

- Random, time-dependent or failure soon after being put into use (infant mortality).

The common causes of instrument faults are:

4.1 Improper Operation in usage

- due to not inadequate training

- not following procedures

- ignorance

- lack of exposure

4.2 Incorrect Installation

Can result in incorrect measurements or malfunction which can be costly and time consuming.

4.3 Careless handling and misuse

Improper handling, storage and misuse

.

This could include

-damage during transportation or movement ,

-accumulation of dust,

-operation under harsh environments

-Spillage of corrosive substances

-leaving instrument powered /on for extended period of time.

4.4 Ageing

-Mechanical parts wear and tear,

-Electronic components like transistors age, wear out or degenerate

These parts need to be replaced in time by qualified, experienced and skilled personnel.

4.5 Poor design or construction

Inherent weaknesses or defects due to

- poor designs

- construction using low quality materials or components

- or bad processes can results in failure of instruments in usage.

4.6 Environment

- Physical (temperature, humidity, pressure, vibration etc) chemical (gases, acids, alkalis) and

- biological (fungi), factors can cause instrument to fail.

- Electrical and pneumatic power fluctuations or lightning may also lead to failures.

5. Repair & Maintenance

5.1 Repairs

- This is corrective maintenance done on an instrument which has broken down.

- This entails faultfinding or trouble-shooting and then fixing the problem.

5.2 Equipment Maintenance

- Maintenance is a process of keeping an instrument in a state fit for carrying out measurements by either

- preventing it from failing to function properly or

restoring it to the desired proper operating state after failure.

- Maintenance includes tests, measurements, adjustments, and parts replacement, performed specifically to prevent faults from occurring.

Benefits to preventive maintenance: Prevention of downtime Ensure instrument is performing according to

the manufacturers’ specification. Extend the useful life of the instrument Avoid premature capital expenditure Less probability of a costly breakdown More reliable instrument Increased likelihood that the instrument will

maintain its specifications Minimization of potential contamination issues A safer instrument for staff

5.2.1. Preventive Maintenance (planned)

This is planned maintenance aimed at the timely overcoming of the causes that lead to operational degradation of an instrument.

It can either be:– scheduled or – condition based (predictive)

maintenance.

5.2.1.1 Scheduled Maintenance

-Periodic, planned, regular and routine

- Carried out on a functioning instrument or system to forestall the occurrence of a breakdown which may occur in future

-The daily, weekly, monthly, quarterly or yearly

5.2.1.2 Condition based or Predictive Maintenance

- This entails optimum or continuous monitoring of selected characteristics - vibration, pressure, temperature etc. - of sensitive and critical instruments

- to predict or detect deviant abnormal occurrences

- offers cost savings over routine or time-based preventive maintenance because tasks are performed only when warranted.

5.2.2 Corrective (unplanned/ breakdown / curative) Maintenance

- This maintenance is carried out when an instrument has ceased to work or broken down.

- It is corrective in that action is taken after actual failure.

5.2.3 Modification

modified or improved by

- change to the design or

- substitution of parts with better ones.

This may be due to the need to

-avoid repeat of earlier critical failure,

-reduce the frequency of failures,

-access to better parts and components

-or the extension or conversion of the use of the instrument.

6.0 INSTRUMENT WRITE-OFF, DISPOSALS OR REPLACEMENT

Instruments may be written-off, replaced or put out of service when :

-when it is no longer cost-effective to maintain/operate -non-availability of spare parts, -obsolete technology,- legal - regulatory requirements, -lack of know-how,-lack of qualified and competent personnel, -advances in technology or policy -environment safety concerns, -design concepts like inbuilt obsolescence, -operating costs

6.2 Disposal

This may be through sale, scraping, donation or relocation.

INSTRUMENTATION AT KEBS

Primary responsibility:

-Repair and maintenance of test, measurement and analytical instruments and equipment.

-Design and development

-Installation and commissioning

EQUIPMENT SERVICED

These include:

-Laboratory equipments/Instruments such as:

- Carbon sulphur analyzers - Photometers,

- Autoclaves - Chromatographs

- Ovens - Echographs

- Polarimeters - X-ray equipment

- Electronic/mechanical analytical balances

- Testing machines (textile, tensile, compression, hardness, etc.)

- Spectrophotometers

Industrial instruments such as:

-Industrial weighing scales/machines

-Process monitoring and control instruments e.g. temperature controllers,

-X-rays equipment,

-tensile and compression testers

Telecommunication Instruments :

- Oscilloscopes

- Signal generators

- Pulse generators

- Power meters

- Spectrum analyzers

Commercial and Trade Instruments such as:

-Flow meters (water meters etc.)

-Energy meters, etc

ENGINEERING /MECHANICAL WORKSHOP

3.1 Preparation of samples

Samples prepared include: -

- Welding rods, tensile and impact samples

- Chippings for chemical analysis

- Hardness test samples

- Other samples

3.2 Support primary calibration laboratory.

- Machining and fabrication of spare for equipment e.g. adaptors for pressure testing.

- Engraving of dipsticks and scales in volume measurements.

- Design and development of testing rigs required in calibration e.g. a tensiometer Force laboratory,

- Development of calibration benches e.g. in Photometry lab

3.4 Fabrication works

- Fabrication of metallic doors, barriers widow grills etc

Machining Work and Other Metal Works

Some of the main machines found in the section are:

- Lathe machines

- Milling machines

- Welding machines

- Engraving machines

- Power saw

- Guillotine machines

- Grinding machines e.t.c.

THANK YOU