GUIDE TO PURCHASE, INSPECT AND MAINTAIN DIGITAL MEASURING INSTRUMENTS  

Three main types of digital measuring instruments----digital calipers, digital micrometers and digital indicators are more and more popular for their high accuracy, multi-function and easy way of operating. Especially in recent years, with its stable quality, competitive prices and continuous coming-out of new products, the market is in a growing and rapid demand.

Digital measuring instruments represented by digital calipers have been produced and used for more than ten years. At present, more than ten manufacturers produce them. In 2000, its domestic overall volume of sale reached 400,000 pieces. Among them, Guanglu products account for 50% of the volume sale. In many respects, such as quality, volume of sale and types, especially, the production of Digital Measuring Instrument for special purposes, Guanglu takes the lead in domestic market.

The following is a brief guide on its operation, verification and maintenance for Digital Measuring Instrument represented by Digital Measuring Caliper and Digital Measuring Indicator.

A.   The guide to purchase Digital Measuring Instrument

    At present, three-button digital measuring instruments with a manual on/off power switch is very popular in the market. Three buttons are respectively for Metric/Inch system interchange at any position, manual on/off power and zero setting at any position. Digital Measuring Caliper of this type can turn on /off manually without its zero position being changed. LCD display screen is made of special quartz glass, not of ordinary organic glass , so the three-button digital measuring instrument produced by Guanglu is anti-scratching and can undergo scratching of an ordinary knife. The modular structure makes it easy to maintain.

Guanglu can produce Digital Measuring Instrument with many selective functions as well as special operative performance at different requests from clients.

    Special functions of Circuit:

Data Holding: Press HOLD Button to hold its momentary measured value when its value is difficult to obtain.

Setting Tolerance Range: The deviation value of limitation at the upper end and the lower one of a measured item can be set. Also, correctness of measured value of a workpiece can be displayed in advance. If it’s not correct, the deviation value above the upper end or the one above the lower end can be shown.

Tracing Maximum Value: With this function, it’s easier to measure the inside diameter such as a hole.

Tracing Minimum Value: With this function, it’s easy to measure the outside diameter such as an axletree.

Display Predetermination:

Usually, the diameter of a hole is measured by inside arch jaws of a vernier caliper. And data-determination is taken from the sum by measuring results and the whole width of inside arch jaws. The negligence in adding its dimension might cause rejects. The diameter of a hole can be obtained directly through data-predetermination, namely, predetermining the combined width of inside arch jaws, which makes it more safe and convenient to operate.

Digital caliper designed mechanically:

Digital Caliper with carbide tipped measuring faces:

It helps its measuring faces against abrasion greatly..

Gear digital caliper: It’s made to measure thickness of a gear tooth in a fixed string. The measuring face is tipped with carbide.

Whorl digital caliper: It’s made to measure the medium diameter of a whorl.

Inside groove digital caliper: It’s made mainly to measure the diameter of a workpiece’s inside groove.

Inside groove digital caliper: It’s made mainly to measure the width of a hole’s inside groove and the position to which a groove directs. Also, digital depth gages with a hook can function as good as above.

Outside groove digital caliper: It’s made mainly to measure dimension of recess on a surface of an item or to measure thickness of a irregularly-shaped board .

Digital thickness caliper: It’s made mainly to measure thickness of a softer item such as rubber and sponge etc. It’s with a power-limit device sometimes.

Offset digital caliper: It makes it easier to measure the stepped sections with a main scale jaw sliding up and down,.

Center distance digital caliper: It’s used to measure the center distance of two holes. 

There’s two types: one is with awl anvil which is used to measure the center distance of two even holes. The other one with cylinder anvil measures an item in a stepping way like this: First, to measure the shortest distance between the inside of two holes, you need to lock the right slider at the right end and fasten and move the left slider to connect with the right slider; secondly, to measure the longest distance between the inside of two holes, you need to lock the left slider at the left end and fasten and move the right slider. With this, the measured value is the sum of the value measured twice. The value of Digital Caliper of this type is half displayed, namely, the distance of axises between two holes can be read out directly. For more information, please refer to its operating instructions.

Universal groove digital caliper: It’s made mainly to measure the inside width of a universal groove and its relative position.

Plastic digital caliper: It’s made of carbon-fiber plastic or of other engineering plastic. Guanglu digital calipers are also made of aluminum alloy etc., which is used mainly on some occasion requiring careful handling to avoid scratching a measured item.

Digital compasses: It took the place of the outdated compasses in time of production for years.

Digital calipers of various types mentioned above bring great convenience in many situations. For full information, please contact the manufacturer.

To purchase or to place an order with a manufacturer, you need to provide a draft of relative parts of the measured workpiece and to point out the dimension which are to be measured as well as its relative dimensions so as to make a selection from the products available properly or to design and manufacture special digital measuring instruments for special purposes. For instance, when it comes to choose and purchase inside groove digital calipers, you need to indicator the diameter of a measured groove within a hole or of the one-side depth, of the width of a groove, of the distance between the groove and of the opening of a hole and its diameter at the opening of a hole so as to make your purchasing or the design by a manufacturer more easier and correct.

B.  The guide to choose and purchase Digital Indicators

.      According to its resolution, digital measuring instruments can be grouped into three types: Digital Indicator, Digital Micrometer and High-accuracy Digital Indicator. Actually, in most cases, a high-accuracy digital indicator can function as the same as a digital micrometer. Also, it can take the place of an expensive digital micrometer at a lower price. Usually, a common digital micrometer ranges over 10mm. A big one ranges over 15mm while a small one ranges at 5mm more or less.With its function of tracing minimum value, it can be used together with an inside groove indicator more conveniently.

According to its main structure, digital indicators can be grouped into a circular digital indicator and a rectangular digital indicator. Most of the rectangular digital indicators are horizontal. You can make a selection at your option.

C.  Verification

Standards available for reference as follows:

GB/T14899—94 is a Chinese National Standard for Digital Caliper.

ISO/DIS13385—96 is an International Standard for designing of Digital Caliper and technical requirements of Metrology. The former standard is applied in most of the state-run enterprises in China; while the latter one is applied in overseas markets and in most of the foreign-funded enterprises in China. ISO/DIS13385-96 is a stricter international standard. It requires cautious verification for errors of a value measured when an inside measurement (like measuring the diameter of a hole) is done. The reason is very simple for that. When measurement of the diameter of a hole (especially a small hole) is done by a new digital caliper, an uncertainty in value should be assured. GB/T14899—94 Chinese National Standard is followed by old national standard largely. It only verifies the deviation of inside measuring jaws and parallel level of measuring faces without verifying the measured value of “inside measuring”. So much consideration has been given to leave leeway in advance for its loss of abrasion that the exactness of “inside measuring” is ignored and that serious measuring error is often made when the diameter of a hole (especially the diameter of a small hole) is measured by a new digital caliper. It makes it more difficult for manufacturers who adopt Chinese National Standard before 1996 to carry out ISO/DIS13385—96 (International Standard). In order to be in accordance with the standard of international markets, Guanglu has been carrying out the above-mentioned international standard most of the time except when it’s not required by some special domestic clients.

D.  Operating Instructions:

1) Before using, clean the surface of the protective sticker of digital measuring instruments for several times with dry, clean cloth to remove water which might congeal.

Because water is weak electrolyte, the ionization of pH indicator and hydroxyl ion can be made. The ions will weaken or destroy capacitive signals to such extent that display will be in a state of disorder. So much attention should be paid to it in wet condition. At present, waterproof digital calipers have been put on the market, but it’s high in price.

2)Working Environment: Temperature:5-40 degrees; Relative humility: below 80%. Under such environment, it can prevent liquid containing eletrolyte from wetting the protective sticker.   .

3) Never apply any electric voltage on a digital caliper or scribing on it by a electroprobe for fear that its circuit is destroyed.

4) Zero Adjusting:

   Clean measuring faces( by rubbing a clean piece of paper between measuring faces for several times) and connect one measuring face with another. Exert pressure of about 3-5N between measuring faces. The measurement can be done upon setting zero by pressing Zero-setting Button. The pushing force exerted in zero-adjusting should be equivalent as far as possible to the one exerted in time of measurement in order to reduce measuring error.

5) Measuring Instruction:    

   Usually, Absoluste measurement is taken. “Zero” is set as mentioned above.

   Difference measuring is usually taken to improve the accuracy in measurement. First, to place a block gage (about a size of a measured item) or to place other workpiece of standard size) between measuring faces with proper pressure (3-5N) and then set relative zero position with Zero button. The difference of standard size is displayed in time of the measuring of an item (Because the difference of value is small, it’s usually called difference measuring). The sum of difference and the above-mentioned standard size is the actual size of the measured item or the absolute size.

6) Data Outputting and Processing

At present, most digital calipers in China have a data port for data-outputting. It can be seen by taking off a small cap on the case of a slider. Meanwhile, it can be connected with a PC or a printer for data-processing or for the printing of analytic chart of measured figures via special cable. So the data port is usually termed an adaptor.

Interface working way: Synchronous serial.

Data: Binary code, 24 bits. Each datum will be transferred twice. The cycle is 300ms (20ms in fast reading state). Transmitting time: 0.5ms.

  Four wires (from left to right): Negative power(-), Clock pulse CP, Data D, Positive Power(+). 
  Pulse range of data: 0 Level≤0.2V, Level ≥1.3V.  
  Clock Pulse CP: 90KHz, effective for high electrical level. 7) Replacement of battery

   Abnormal display (digits flashing or even no display) shows a flat battery. A 1.55V silver oxide button cell (SR44) should be replaced.

   The reason that a battery bought from a market doesn’t work satisfactorily lies in the automatic discharges of the battery and the wearing-down of its power. To get it solved, you may contact without hesitation the supplier for mailing of new batteries. Guanglu promises to provide domestic clients with batteries free of charge within three years.

E.  Maintenance
      
        At present, digital calipers in the market seldom act up. The problems which clients are faced with usually result from its wearing-down of batteries, from its poor contact or from the breakdown as follows;

1) “Fixed digits” ---- resulting from accidental trouble in circuit, accompanied by display of some irrelative signs.

Solution: Take out the battery and put it back after over 30 seconds. It’ll become normal after several trials.

2) Flashing digits---- resulting from low electric voltage. To get it solved, you need to replace the battery as soon as possible.

3) Figures displayed in disorder-----resulting from its unstable display. It results from the wet protective sticker. To get it solved, please refer to the above-mentioned operating instructions.

4) Mechanical abrasion:

 The method of repair is about the same as that of a vernier caliper’s. But see to it that it must avoid forceful striking. And its striking should be done after the electronic parts are taking apart. Repair can also be done for more times than before not only because “Zero” can be set at any position but also because it’s not limited by zero- error of vernier calipers. It’s worth great noticing that repair is  becoming more and more difficult due to the fact that the left end of an ordinary four-way digital caliper acts as the step measuring face and that the end of inside jaws are hard and crisp. At clients’ request, we  can solve that problem using anti-jaw-broken technique which is one of the patents of Guanglu.. Guanglu also suggests the maintenance of all digital calipers made by different manufacturers in China free of charge. And the replacement of parts will be charged reasonably. Domestic clients are welcome to enjoy that service.