DVOM NotSo Basics Digital High Impedance VOM Meter

DVOM Not-So Basics

Digital High Impedance VOM

Meter Selection Features • Voltage DC V • DC is Direct Current • Reads the circuit pressure • Best meter for troubleshooting • Voltage AC ~ V • AC is Alternating Current • Use for Magnetic Pickup Outputs

Meter Selection Features • Diode Check • Applies voltage to turn on Diode in Forward Bias • . 3 to. 5 v in one direction and OL in the other means the diode is OK • Resistance / Ohms Ω • Last meter to use • OL is open or over the range of the meter • 0. 1 – 0. 3Ω circuit is shorted or completed

Meter Selection Features • Frequency Hz • Measures the Hertz or pulses, cycles per sec. • Percent Duty Cycle % • Measures the percent “on” time for Pulse Width Modulated signals • Continuity Buzzer • “Beep” to indicate continuity (maybe) • Be careful – some meters will sound at 100Ω

Meter Selection Features • Amperes (Amps) A • Measures the current through the circuit • CAUTION - The probes complete the circuit • Milli. Amperes m. A • Same as Amps only lesser current • Auto Range • Auto is easier – Manual is harder

Digital High Impedance VOM

Probe Sockets • COM Black cord goes here • VΩ Red cord here for Voltage and Resistance • A • Red cord here for Amps – 10 A - 20 A • Fuse Protected • m. A • Red cord here for Lower Amps • Protected with a smaller fuse

Probe Safety

Voltage Check 1 12. 5 v M 12. 5 V - + Open Since there is no current flow, there is no voltage drop

Electricity Compared to Hydraulics 12. 5 • Voltage = Pressure V - + . 15 • Current = Flow (gpm) A - + 240 • Resistance = Restriction Ω * Electricity behaves very much like fluid * +

Electricity Compared to Hydraulics Battery = Reservoir + Pump Voltmeter = Pressure Gauge Ammeter = Flow meter Load/Resistance = Load/Restriction * Electricity behaves very much like fluid *

Pressure Check 1 1000 psi Pump w/1000 psi internal relief valve Control valve P 1000 psi Motor M 1000 psi Reservoir Since there is no flow, there is no pressure drop blocked

Voltage Check 2 12. 5 v Completed Circuit M 12. 5 12. 47 0. 00 12. 45 V - + 1200 RPM Voltage Drop is normal on Non-Load components as long as the maximum drop is ≤ 0. 5 v on 12 v systems

Pressure Check 2 1000 psi Pump w/1000 psi internal relief valve Control valve P 998 psi Motor M 0 psi Reservoir Minor pressure drops across Non. Load components are normal 1200 RPM

Voltage Check 3 12. 5 v Green Connection M 12. 5 12. 47 9. 45 V - + 300 RPM Voltage Drop that is Significantly less than full system voltage indicates High Resistance

Pressure Check 3 1000 psi Pump w/1000 psi internal relief valve Control valve 275 psi Motor P Reservoir M Major pressure drops across Non-Load components indicate restriction 300 RPM

Pressure Check - Example 20 psi P 18 psi 0 psi Pressure drop across filter indicates the level of Restriction Tank

Other Concepts of Operation • Ghost voltage & zero voltage indicate opens and shorts and can be used in place of an ohmmeter • A digital VOM will indicate full system voltage, even through high resistance • Continuity buzzer will buzz or beep even if there is up to 100Ω in circuit – must check ohms to verify • Circuits must be isolated to check ohms

Ghost Voltage Ghost The meter is so sensitive that it is picking up voltage from the atmosphere V - + Your body even generates an electrical field!!

Ghost Voltage 0. 00 V - + This is eliminated by touching the probes together giving you Zero volts.

Voltage Check 4 12. 5 v +- 0. 00 V - + 0. 00 If the meter reads “True Zero” you have Continuity V - +

Voltage Check 5 12. 5 v Open Connector +- Blown Fuse Ghost V - + Ghost Voltage indicates that you have an Open Circuit Ghost V - +

Voltage Checks Review 12. 55 Could you make these checks with an Ohmmeter? ? V - + 12. 55 V Ghost V - 0. 00 + V - +

Voltmeters 12. 5 v V - + Voltmeters are the safest of all meters. They don’t complete the circuit. The meter has an extremely high internal resistance or impedance and therefore draws extremely low amperage. Low Amps – Low Danger.

Other Concepts of Operation • Ghost voltage & zero voltage indicate opens and shorts and can be used in place of an ohmmeter • A digital VOM will indicate full system voltage, even through high resistance • Continuity buzzer will buzz or beep even if there is up to 100Ω in circuit – must check ohms to verify • Circuits must be isolated to check ohms

High Resistance 12. 55 Without Current Flow There is No Voltage Drop V - + 12. 55 V - + Corroded Terminal

Voltage Check 3 12. 5 v (Review) Green Connection M High Resistance causes a Significant Voltage Drop but only if there is Current Flow 9. 45 V - + Problem: How do I insert the meter’s Probe into the circuit?

Why NOT to Puncture the Wire 1. Puncture the Insulation Moisture 2. Remove the Probe, a Hole is Left 3. As the Wire Heats, the Hole allows the Insulation to Expand 4. As the Wire & Insulation Cools and Heats, it Draws in Moisture thought the Opening 5. Corrosion Develops

High Resistance Checking Tool TESlite Voltmeter Leads TESlite ® Enhanced Voltmeter Leads - www. teslite. com

High Resistance Checking Tool Without Current Flow there is No Voltage Drop 12. 55 3. 75 Corroded Terminal V - + TESlite ® Leads 12. 55 V PUSH the Button Now a Circuit is Completed, there is Load, Current flows and Voltage Drop can be read

First Corrosion Check Corrosion 12. 55 v 4. 75 v V - 1. Remove load 2. Test across Load Connection 3. Low Voltage – Bad Circuit M 4. Retest w/ Good Ground + 5. Low Voltage – Power Circuit is Bad 6. If Good Voltage – Ground is Bad M

Power Side Corrosion Check Corrosion 12. 55 v 3. 78 v 12. 53 v 12. 52 12. 55 v M V - + TESlite ® Leads

Ground Side Corrosion Check 12. 55 v 12. 53 v 4. 75 v V - + M Corrosion

Other Concepts of Operation • Ghost voltage & zero voltage indicate opens and shorts and can be used in place of an ohmmeter • A digital VOM will indicate full system voltage, even through high resistance • Continuity buzzer will buzz or beep even if there is up to 100Ω in circuit – must check ohms to verify • Circuits must be isolated to check ohms

Continuity “Beeper” To safely check for Continuity, use the Ohmmeter function or Voltmeter, don’t trust the Beeper BEEP 0 10 Ω 100. 0Ω Ω - +

Other Concepts of Operation • Ghost voltage & zero voltage indicate opens and shorts and can be used in place of an ohmmeter • A digital VOM will indicate full system voltage, even through high resistance • Continuity buzzer will buzz or beep even if there is up to 100Ω in circuit – must check ohms to verify • Circuits must be isolated to check ohms

Ohmmeter Limitations • For an Ohmmeter to work accurately you MUST isolate the circuit – EVERYWHERE HOW? ? ∞ • “OL” or indicates that the meter is not able to read the resistance in the circuit. Go to a higher scale. • Ohmmeters use about 3 volts to operate – over 50 feet of wire this is not much to work with • Minimum Resistance is usually about 0. 3 – 0. 5 Ω which can approach actual values on some components

Ohmmeters OL 2. 03Ω 254. 0Ω 87. 0Ω Sensor Ω - + Ohmmeters are used for checking separate components for shorts, opens or proper values. However, it is not the best troubleshooting tool for circuits. M Relay Motor

Troubleshooting Relays 75 – 110 Ω Coil Resistance (12 V Estimates) 87 A 87 86 30 85 30 87 87 A 86 20 – 40 Ω 85 ~ 130 Ω

Why use a Relay? ? If I Short 87 to 30 What Would Happen? 12 V+ 87 87 87 A 85 30 87 87 A 86 86 30 Horn 30 86 (Socket) 85 87 A (1Ω) 85 (80Ω) A Volt Meter across Socket positions 85 & 86 should show what when the switch is closed ? 85 & 86 = Coil 30 = Common 87 = N. O. 87 A = N. C. A=V/Ω Ohm’s Law Switch A=12/80 =. 15 A Horn A=12/1 = 12 A

Troubleshooting Relays (Base of Relay) 87 87 A 86 85 30 With the Battery Across 85 & 86 30 to 87 Should Read 0Ω 30 to 87 A Should Read OL With the Battery Removed 30 to 87 Should Read OL 30 to 87 A Should Read 0Ω 87 A 9 Volt 87 86 30 85

Troubleshooting Micro Relays (Base of Relay) With the Battery on Brass Pins Copper Pins Should Read 0Ω With the Battery Removed Copper Pins Should Read OL 9 Volt

Ammeters 9. 0 a A - + M Ammeters complete a circuit. It is a jumper. Whatever is connected will become active. It is therefore the most dangerous meter. The meter is protected with a fuse but you aren’t. Amps Kill.

Relay Amperage Ratings 12 V 30 A/40 A Coil Voltage - 12 Volts 85 30 87 87 A 86 30 A for N. C. Contacts 40 A for N. O. Contacts

Checking Amp Flow with a Compass Align the needle with the cable to start Current Flow Crank Negative Magnetic North Run We just proved that the alternator is charging Power Off On Solenoid Electro-Magnetic Actuator

Arc Suppression in Relays - + + ( 700Ω ) No Polarity The Diode Points to the Positive Wire 85 30 87 87 A 86