Electrical lab for LHAP

LHAP 302 Irrigation Electrical Lab Students: ____________________________________________________ ____________________________________________________ In this lab you will investigate the use of a DIGITAL MULTIMETER and the tests that are performed on irrigation system wiring. Get to know the settings on the multimeter: Sine wave + V = Volts AC solid line + dashed line underneath = Volts DC “omega” (horseshoe like) = Resistance Follow the steps outlined below for safe operation of the irrigation controller and the digital multimeter: TEST #1 - VOLTAGE NOTE: Volts both AC and DC are measured with the POWER ON. 1.Plug in the test leads to the multimeter as follows: the red lead into the + jack (also labeled with V “omega” A)’ the black lead into the middle or “com” jack Turn on the multimeter and set it to volts AC Set it to the highest reading. If you set it too low you will cause damage to the meter. Plug in the irrigation controller Hold the black lead of the multimeter on the “COM” terminal screw in the controller Hold the red lead of the multimeter to one of the numbered stations terminal screws Using the operation manual, set one of the stations to run manually. Record the # of volts that the controller produces for the station _______________ Volts Volts both AC and DC are measured with the power on. TEST #2 - CONTINUITY The continuity test will help you check for shorted or open electrical circuits. Plug the black lead into the -COM jack and the red lead into the + V”omega”A jack. Press POWER to turn on the multimeter. Set the function switch to “omega” resistance setting TO PREVENT METER DAMAGE, IT IS VERY IMPORTANT THAT YOU DO NOT TOUCH A LIVE VOLTAGE SOURCE WHEN THE METER IS IN THIS MODE. Set the dial to the lowest setting in this area (200) Disconnect the common wire and the control wire from the controller 6. Hold the black probe to the common wire and the red probe to the field wire Take a reading of your results ______________________ ohms TEST #3 - RESISTANCE The following procedure will test the health of an irrigation solenoid. You will be using the omega “resistance” setting on the multimeter for this test. TO PREVENT METER DAMAGE, IT IS VERY IMPORTANT THAT THE CIRCUIT POWER BE TURNED OFF WHEN MEASURING RESISTANCE. Set the multimeter to center position or the position that shows the “omega” symbol. Set it to the lowest reading (200) in this area. Turn on the multimeter and place one lead to one of the wires coming from the solenoid Place the other lead of the multimeter on the other solenoid wire Record your result: ______________ohms If your reading is zero or “OL” (overload) then your solenoid is defective. TEST #4 - TRANSFORMER Transformers can also be tested using a multimeter. You will be testing for resistance in the wiring - the same as you do for solenoids. TO PREVENT METER DAMAGE, IT IS VERY IMPORTANT THAT THE CIRCUIT POWER BE TURNED OFF WHEN MEASURING RESISTANCE. ( to be performed only on plug end transformers) Disconnect the plug of the controller from the wall socket. Plug the black lead into the -COM jack and the red lead into the + V”omega”A jack. Select the “omega” setting on the multimeter. Touch the leads from the multimeter to the ends of the plug on the transformer. You will either get a resistance reading showing that the windings are intact or an open reading that indicates that the transformers internal fuse is bad and needs replacing. Transformer reading ______________ **If you get any reading your transformer is good. A zero, 1 or OL reading is a faulty transformer Readings normal resistance reading 20-60 ohms short circuit - low ohm reading (below 10) open circuit - 1 or OL partial open (bad splice) high ohm reading DC latching solenoids 4-15 ohms black - common, red - hot Types of problems Open - broken wire (cut or splice came apart) -no response from the controller-pump damage Short - blown fuse-tripped breaker- bare wire touching ground Transformer - loose wire connection slow burn -old solenoid starting to go bad partial burn - electrons flow on outer edge of wire, corrosion pulls wire apart get arching and a high reading Partial Open - bad or poorly made wire splice- old or corroded splice 90% of electrical problems are a result of poor wire splices