1. DVOM Not-So Basics

2. Digital High Impedance VOM

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

4. Meter Selection Features
Diode Check
Applies voltage to turn on Diode in Forward Bias
.3 to .5v 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

5. 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

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

7. Digital High Impedance VOM

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

9. Probe Safety

10. Since there is no current flow, there is no voltage drop
Voltage Check 1
12.5v M
Open V
Since there is no current flow, there is no voltage drop
12.5

11. Electricity Compared to Hydraulics
12.5 V
Voltage = Pressure
Current = Flow (gpm)
Resistance = Restriction
.15 A
240 Ω
* Electricity behaves very much like fluid *

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

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

14. Voltage Check 2
Completed Circuit
12.5v
Voltage Drop is normal on Non-Load components as long as the maximum drop is ≤ 0.5v on 12v systems M
12.45
12.5
12.47
1200 RPM
0.00 V

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

16. Voltage Check 3
Green Connection
12.5v M
12.47
9.45
12.5
300 RPM V
Voltage Drop that is Significantly less than full system voltage indicates High Resistance

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

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

19. 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

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

21. Ghost Voltage
This is eliminated by touching the probes together giving you Zero volts.
0.00 V

22. If the meter reads “True Zero” you have Continuity
Voltage Check 4
12.5v
+ - V V
0.00
0.00
If the meter reads “True Zero” you have Continuity

23. Ghost Voltage indicates that you have an Open Circuit
Voltage Check 5
Open Connector
12.5v
+ -
Blown Fuse V V
Ghost
Ghost
Ghost Voltage indicates that you have an Open Circuit

24. Could you make these checks
Voltage Checks Review
Could you make these checks
with an Ohmmeter?? V
12.55
12.55 V V
Ghost V
0.00

25. Voltmeters
12.5v 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.

26. 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

27. There is No Voltage Drop
High Resistance
Without Current Flow
There is No Voltage Drop V
12.55
12.55 V V
12.55
Corroded Terminal

28. Voltage Check 3 (Review)
Green Connection
12.5v M
High Resistance causes a Significant Voltage Drop but only if there is Current Flow
Problem:
How do I insert the meter’s Probe into the circuit? V
9.45

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

30. High Resistance Checking Tool
TESlite Voltmeter Leads
TESlite ® Enhanced Voltmeter Leads -

32. High Resistance Checking Tool
Without Current Flow there is No Voltage Drop V
12.55
3.75
PUSH the Button
12.55
Corroded Terminal
TESlite ®
Leads
12.55 V
Now a Circuit is Completed, there is Load, Current flows and Voltage Drop can be read

33. First Corrosion Check Corrosion 12.55v Remove load
Test across Load Connection
Low Voltage – Bad Circuit M M
4.75v
4.75v V
Retest w/ Good Ground
Low Voltage – Power Circuit is Bad
If Good Voltage – Ground is Bad

34. Power Side Corrosion Check
12.55v V M
12.52
12.53v
12.55v
3.78v
TESlite ®
Leads

35. Ground Side Corrosion Check
12.55v V
12.53v M
4.75v
Corrosion

36. 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

37. Continuity “Beeper”
To safely check for Continuity, use the Ohmmeter function or Voltmeter, don’t trust the Beeper
100Ω
BEEP Ω
100.0Ω

38. 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

39. Ohmmeter Limitations HOW??
For an Ohmmeter to work accurately you MUST isolate the circuit – EVERYWHERE
“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
HOW??

40. However, it is not the best troubleshooting tool for circuits.
Ohmmeters Ω
Ohmmeters are used for checking separate components for shorts, opens or proper values.
However, it is not the best troubleshooting tool for circuits.
87.0Ω
2.03Ω
254.0Ω OL
Sensor M
Motor
Relay

41. Troubleshooting Relays
12V
75 – 110 Ω
Coil Resistance
(12V Estimates)
ACME
87A
20 – 40 Ω
~ 130 Ω

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

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

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

45. Ammeters
9.0a A
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. M

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

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

48. Arc Suppression in Relays
12V
The Diode Points to the Positive Wire
( 700Ω )
No Polarity