Using the B Digital Multimeter in the Home by James Bryant A digital multimeter, sometimes known as a digital voltmeter or DVM slightly inaccurately as it measures amps and ohms as well as volts , is an instrument which is used for making electrical and electronic measurements. There are many different types, with widely varying accuracies. This means that you can measure changes of voltage of one two thousandth of the maximum, but the actual accuracy of the measurement is only one hundredth of the maximum. The B is made by several manufacturers and sold under many brand names. It may be called the DTB, the MB or other varients on its number, and its case may be yellow commonest , black, or even more exotic colours. It is easy to make such measurements and they can save hours of frustration.
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Using the B Digital Multimeter in the Home by James Bryant A digital multimeter, sometimes known as a digital voltmeter or DVM slightly inaccurately as it measures amps and ohms as well as volts , is an instrument which is used for making electrical and electronic measurements. There are many different types, with widely varying accuracies. This means that you can measure changes of voltage of one two thousandth of the maximum, but the actual accuracy of the measurement is only one hundredth of the maximum.
The B is made by several manufacturers and sold under many brand names. It may be called the DTB, the MB or other varients on its number, and its case may be yellow commonest , black, or even more exotic colours. It is easy to make such measurements and they can save hours of frustration.
Every household should have one. Fitting the Battery Before using the meter it must be fitted with a small 9V battery. It is best to use an alkaline one as they have a longer life and are less likely to corrode.
Unscrew the two small Philips screws in the back of the case and lever up the bottom of the case to fit the new battery - before replacing the back and the screws check that the fuse is OK as well. The battery will last for two or three years with occasional use, but only for about two to three weeks if the meter is left turned on - so it should be turned off when it is not in use by rotating the switch so that it points upwards.
Note that when the meter is off there is no visible display - the screen is a uniform grey - and when the battery needs replacing when its voltage has dropped to about 7 V the warning BAT appears in the upper left-hand side of the screen in addition to the normal display while the meter is turned on.
Fitting the Leads In use the black lead is plugged into the lowest of the three sockets unsurprisingly the black one and the red lead into the centre socket the lower of the two red sockets. The red lead should never be plugged into the other red socket except to measure large DC currents up to 10 amps. It is possible though unlikely that incorrect connection of the red lead may cause damage to batteries being checked or to the meter itself.
The Internal Fuse It is also possible to damage the meter if it is switched to current measurement while it is connected to a battery or other voltage source - this will often blow the internal fuse. If this happens the meter will still have a display, but it will not work - it will simply show zeros or over-range on the resistance ranges no matter what is connected to it.
In such an eventuality the back must be removed and the fuse replaced with a new one. See the diagram in the "Fitting the Battery" section above. Sadly, the manufacturers often fit larger 1A or 3A fuses in new meters because they are cheaper, but mA is the correct rating.
When the leads are not connected to anything you should see an open-circuit display as shown. Now touch the leads to opposite ends of the fuse. Throw it away at once - it is easy to keep a blown fuse and use it instead of a good one at some time in the future. Before fitting a new fuse check that it is indeed a good one. They can fail in two ways - they may break internally, either at a connector or somewhere where they have been stressed, or they may develop a short-circuit i.
The DVM can check for both problems but the wires must be isolated while they are tested - never check a wire or cable while it is connected to anything, in particular to any power source. To check continuity i. See the meter diagrams for fuse testing. Now touch the leads to opposite ends of the wire or cable.
Simple wires contain one conductor and are tested once. Many cables contain two or more conductors and the continuity of each one must be tested separately. If all of them are good you should then check the cable for short circuits. Again check correct operation - when the leads are not connected to anything you should see the open-circuit display and if the leads are touched together you should see a display of zero.
Now check for short-circuits. It is necessary to check for possible short circuits between every pair of wires in the cable - if there are only two or three wires this is easy, but if there are a larger number it is important to be methodical to ensure that no pair is overlooked.
The best way is to join all the wires together electrically, then detach each wire in turn and check for a short circuit between it and all the rest. If you find a short circuit you should check if is in the cable itself or in a connector.
It is sometimes possible to repair a short circuit in a connector unless it is moulded onto the cable , but a cable with a short circuit, like a blown fuse, should be thrown away immediately. This is still a good indication that there is no short circuit. Light Bulbs It is not possible to use the DVM to check modern LED or compact fluorescent light bulbs but you can use it to check if an old-fashioned filament incandescent light bulb has died.
Now touch the leads to the contacts of the incandescent bulb. Light bulb contacts are often dirty - to make sure that you make a good electrical connection to them when making this test use the point of the probe to go through any dirt or corrosion.
As with a fuse, before fitting a new bulb do check that it is indeed a good one. The meter allows you to check the battery when something stops working, and also to check the condition of a new battery before fitting it, since a small but appreciable percentage of new batteries are dead on arrival.
To measure the voltage of a battery turn the switch to DC Volts - the millivolt 2 volt range for single cell batteries except lithium ones - see below , or the 20 volt range for most multi-cell batteries. For the very few batteries with output voltage greater than 20 volts use the volt range. Then touch the probes on the ends of the leads to the connections of the battery.
Ideally the positive lead should go to the positive battery terminal, and vice versa, but it does not really matter - if the leads are reversed the voltage reading is also reversed and the voltage will show as negative. On the millivolt 2 volt range the reading is in millivolts thousandths of a volt and there is no decimal point the reading illustrated is mV which equals 1.
The other ranges have a decimal point and show volts except the m [ mV] range which shows millivolts. Their voltages are the same as the alkaline ones. A new single-cell alkaline battery should have a voltage between 1. A new battery with a voltage below 1. If a device uses several single-cell batteries it is best to use a set of the same type and check that they all have similar not necessarily exactly identical voltages when they are installed.
Multi-cell alkaline batteries may have nominal voltages of 4. When new their voltages should be 4. As alkaline batteries are used their voltage drops gradually over their life. If you test alkaline batteries from a device which is not working and find that single cells have a voltage below 1. Button cells Button cells are the small button shaped single-cell batteries illustrated with the single-cell alkaline batteries above which are often used in small, low-powered electronic devices.
There are an enormous number of different sizes, which I shall not discuss, but four different types: alkaline, silver, zinc-air and lithium there used to be mercury button cells as well but they are no longer manufactured as the materials involved are too toxic.
Silver and alkaline button cells Both silver and alkaline button cells have initial voltages of 1. The difference is that the voltage of the silver based cells remains fairly constant for most of their life and then drops abruptly, while alkaline button cells behave like any other alkaline cell and have a voltage which drops fairly steadily with use.
Zinc-air hearing aid button cells Zinc-air button cells are used for hearing aids. Once the cell is opened to the air by removing the adhesive label from the cell they have a lifetime of only a few weeks, whether or not they are actually used.
Their initial voltage is about 1. New lithium button cells have a voltage of 3 to 3. If they are not used lithium cells have a very long shelf life - sometime as much as 15 years. Single cells will have a higher voltage Rechargeable Secondary Batteries Rechargeable alkaline batteries Some alkaline batteries may be recharged with special chargers note that they must be charged with chargers designed for alkaline batteries - chargers for NiCd or NiMH batteries are not suitable.
Such batteries are labelled "Alkaline Rechargeable" or some near equivalent and have the same initial and end of life voltages as other alkaline cells 1. If you attempt to recharge non-rechargeable alkaline batteries you may find that they leak corrosive caustic potash, explode, or catch fire.
It is wiser not to try. Lithium Ion Li-Ion batteries were already very common in cellphones, cameras, GPS receivers and similar portable electronic equipment but were not generally used as discrete batteries so I did not discuss them. When any of these batteries are made into special battery packs for particular equipment cameras, electric power tools, etc.
You do not usually need a DVM to work with such batteries. Today Li-Ion batteries are supplied in all these formats and the larger cylindrical cell and also in rectangular battery packs of many different sizes, while NiCd batteries are only found in older equipment and are mostly unavailable for sale cadmium is toxic.
Your DVM can help you manage all of these. Much modern electrical and electronic equipment is designed to work well with these batteries and, usually, also with alkaline ones and does not stop working until the voltage drops to about 1. Unlike alkaline cells, the NiMH or NiCd cell voltage does not drop much during discharge until the battery is nearly spent, when it drops quite quickly.
The simplest chargers for these batteries rely on the user knowing how long an exhausted battery must be charged, and if the battery is not fully discharged they may overcharge it, which will reduce its long-term life expectancy.
Voltage measurements with a DVM are of little help in monitoring the state of charge. The MAHA MH-C Smart Charger Smart chargers contain quite complex circuitry which measures cell temperature and rate of change of cell voltage and reliably stops charging at the right moment. It is well worthwhile investing in these more expensive chargers if you expect to make much use of rechargeable NiMH or NiCd batteries.
This is much higher than alkaline or NiMH cells so, even if they are the same size, it is not possible to replace the older types with Li-Ion ones in existing equipment. When freshly charged the Li-Ion battery voltage is about 4. To measure this voltage on cylindrical cells or any cells with just two terminals connect the DVM to the two terminals - polarity does not really matter in this case, if you connect the leads the wrong way round the meter will show a negative voltage but you are still reading the voltage you need to know.
If you have a battery with three terminals, like many cellphone and camera batteries, connect the leads to the outside ones. If the reading is below 1 volt, try connecting between the centre and one or other of the outer ones. All chargers for Li-Ion batteries contain circuitry to prevent overcharging, most of them check for overheating during charge as well, and nearly all of them indicate when the battery has been fully charged - so it is not necessary to worry about leaving Li-Ion batteries in the charger for too long a time.
Lead-acid batteries Cars, motor-cycles and boats, and uninterruptible power supplies, use lead-acid rechargeable batteries. They usually have six cells and give 12 volts, but some small boats and bikes use 6 volts, and trucks and larger boats may use 24 volts. The voltages given in the rest of this section refer to 12 volt batteries and should be divided by 2 for 6 volt ones, or multiplied by 2 for 24 volts.
A fully-charged lead acid battery has a voltage of As the battery discharges the voltage drops, fairly linearly, to about Batteries for cars and motor-cycles are normally kept near maximum charge and are expected to deliver large peak currents for starting the engine. Batteries in boats, motor homes and uninterruptible power supplies may be discharged very deeply - the batteries used for these different applications are different.
Car batteries may be damaged by repeated deep discharges, while deep discharge batteries have lower maximum current. Simple car battery chargers deliver a constant current of a few amps when the battery voltage is below about 13 volts, but above this apply a constant voltage of It is possible to use the DVM on its voltage and 10 A current ranges to measure charge current and battery voltage.
DT830B Digital Multimeter
It has diode and transistor test functions as well. The photographs and circuit diagram in this article may be of interest to engineers who need to repair their meters. This meter has Chip on Board COB package inside, and the designation leads me to believe that this meter has the Intersil ICL single chip solution, or perhaps a variant of that design. This is an affordable pocket meter that works reasonably well for the price.
The Gadget Queen DT-830B User Manual
This is not an auto-ranging meter, and therefore you will have to select the correct ranges for voltage and current measurements. This is one of those meters where you will need to think first to determine what you are measuring. Are you measuring voltage, or current? Is it AC or DC?
Multimeter User Manual [PDF Download]
Histest DT830 Series Owner's Operation Manual