An ammeter is a device that is used to measure the electric current. Now the ammeter can either be digital or analogue. It can be a single range or dual range.
The digital ammeter is one on which there is a screen and you can read the value of the electric current. An example of a digital ammeter is in fig 1 below. It the easiest to use as you just to connect it and read it.
The analogue ammeter is the one that was used in the old days. It has a pointer in it that will indicate the current in the circuit. It is more difficult to use and the chance of committing a parallax error is greater. However it does not require maintenance like the digital ones that require a dry cell in it to work. The dry cell require frequent replacing. Fig 2 below is an example of an analogue ammeter.
A single range ammeter is one that ca measure electric current within a particular range. For example it can measure from 0 to 5 A. However there are ammeters that can measure current on two different range. For example it can measure current on the 0 to 1 A range. However if the current being measured exceed the 1 A vale it can be switched to a higher range like the 0 to 5 A. An examples of a single range ammeter is in fig 3 and that of a double range is in fig 4.
Fig 3 A single range ammeter
Fig 4 A dual range ammeter.
How to use a dual range ammeter?
Most ammeter as you can see above have only two terminals and you just plug the wires in. However a dual range ammeter has three terminals. So how would you plug in the wires in that case? I would take the case of an ammeter that have two ranges 0 – 1 A and 0 – 5 A. If you want to use the 0 – 1 A range then you would connect the wires as in the fig 5 below.
Fig 5 Connecting an ammeter on the first range.
However if you want to connect the Ammeter on the second range then you would have to connect the wires as shown in fig 6 below.
Fig 6 Connecting an ammeter on the second range