GENERAL INFORMATION CU800 Service Manual
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1.19.5 Ammeter
An ammeter measures the flow of current (amps) in a circuit when connected in series in a circuit,
the ammeter determines if current is flowing through the circuit and if that current flow is excessive
because of a short in the circuit. Current flow is often referred to as current draw. Comparing actual
current draw in the circuit or component to the manufacturer’s specified current draw provides useful
diagnostic information.
1.19.6 Self-powered Test Light
A self-powered test light can be constructed from a 12-volt light bulb, a pair of test leads and a
12-volt battery. When the test leads are touched together, the light bulb should go on.
Use a self-powered test light as follows:
1. Touch the test leads together to make sure the light bulb goes on. If not, correct the problem
before using it in a test procedure.
2. Select two points within the circuit where there should be continuity.
3. Attach one lead of the self-powered test light to each point.
4. If there is continuity, the self-powered test light bulb will come on.
5. If there is on continuity, the self-powered test light bulb will not come on, indicating an open circuit.
1.19.7 Ohmmeter
An ohmmeter measures the resistance (in ohms) to current flow in a circuit or component. Like the
self-powered test light, an ohmmeter contains its own power source and should not be connected to a
live circuit.
Ohmmeter may be analog type (needle scale) or digital type (LCD or LED readout). Both types of
ohmmeter have a switch that allows the user to select different ranges of resistance for accurate
readings. The analog ohmmeter also has a set-adjust control which is used to zero or calibrate the
meter (digital ohmmeters do not require calibration).
An ohmmeter is used by connecting its test leads to the terminals or leads of the circuit or
component to be tested. If an analog meter id used, is must be calibrated by touching the teat leads
together and turning the set-adjust knob until the meter needle reads zero. When the leads are
uncrossed, the needle reads zero. When the leads are uncrossed, the needle should move to the
other end of the scale indicating infinite resistance.
During a continuity test, a reading of infinity indicates that there is an open in the circuit or
component. A reading of zero indicates continuity, that is, there is no measurable resistance in the
meter needle falls between these two ends of the scale, this indicates the actual resistance, multiply
the meter reading by the ohmmeter scale. For example, a meter reading of 5 multiplied by the R×100
scale is 5000 ohms of resistance.
CAUTION
Never connect an ohmmeter to a circuit which has power applied to it. Always
disconnect the battery negative lead before using an ohmmeter.
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