Test Equipment

How should you set an ammeter range before measuring current?

Begin with the highest expected current range to protect the meter from damage

What is a multimeter?

A single instrument that combines multiple meters and has both linear and non-linear scales on one face

Why do some meters have a mirrored strip behind the needle?

To eliminate parallax error—if you see a shadow behind the needle

How do you select the proper range on an ohmmeter?

Choose a setting that places the needle between zero and mid-scale for best accuracy

What must you always do before using an ohmmeter?

Zero the ohmmeter to account for the internal battery’s resistance

Why must you isolate a component from the circuit when measuring resistance?

To prevent other current paths from affecting the reading

What happens if you connect an ammeter in parallel with a load?

It creates a near-short circuit because the ammeter’s internal resistance is almost zero

What type of current do standard clamp-on ammeters measure?

They generally measure AC current at 60Hz in Canada (though specialized ones can measure DC)

How can you measure very low current using a clamp-on ammeter?

Wrap multiple loops of the conductor around the clamp to multiply the reading

Why might a circuit fuse keep blowing when measuring current with an ammeter?

Because the meter is inadvertently connected in parallel with the load instead of in series

What should you do if your DC voltmeter needle deflects below zero?

Reverse the meter leads to correct the polarit

What is the purpose and behavior of the thermopile-controlled power unit?

Holds open main gas valve or energizes safety switch

Acts as a solenoid

Resistance around 0.018 ohms

Manual reset button usually required

Must be held while pilot heats up thermocouple

What steps are required for an open circuit mV test on a thermocouple?

Disconnect t/c from control, connect mV meter

Light burner and monitor t/c output

Should be 17–32 mV (usually 28–32 mV)

Over 32 mV = reduce flame (t/c overheating)

Wait 3–4 minutes for stable readings

Only adjust pilot flame during this test

What is the procedure and expected result for a closed circuit mV test on a thermocouple?

Use test adapter to connect meter in parallel with power unit

Light pilot with everything connected

Reading should be 8–17 mV

How can system analysis be performed on a thermocouple setup?

Compare open vs closed mV readings

Used to verify t/c and system condition

Often considered impractical or unnecessary

How do you measure thermocouple response time and what are acceptable limits?

Kill flame and time how long gas valve takes to shut

Max times:

Central furnace: 180s

Standing pilot appliances: 90s

Heavy gases: 20s

400 MBTU/hr appliances: 4s

What is the dropout point and how is it measured?

Point where plunger deactivates circuit

Measured during closed circuit reading

Used as basis for turndown test

How is the turndown test performed on a thermocouple system?

Reduce flame to just above dropout point

Try to light main burner

If successful, flame is adequate

If not, reposition t/c or pilot

Do not increase flame to compensate

Reset flame to open circuit value after test

What is the safety shutdown test for thermocouples?

Disconnect t/c while appliance is running

Ensure main and pilot gas shut off (for 100% shutoff systems)

How are thermopile tests conducted and what values are expected?

Open and closed circuit tests are the same process

On a 750mV thermopile:

Open circuit: 540–800 mV

Closed circuit: 280–410 mV

What is the meaning of pull-in voltage for thermopiles?

Minimum millivolts required to open gas valve to burner

What flame conditions can cause t/c and thermopile failure?

Lazy Yellow Flame

Caused by dirty burner or oversized orifice

Carbon buildup affects detection

Waving Blue Flame

Caused by draft or recirculating POC

Sensor cools off

Small Blue Flame

Caused by low gas pressure or blockage

Sensor cools off

Noisy, Lifting, Blowing Flame

Caused by high pressure or excess air

Overheats and damages sensor

Hard, Sharp Flame

Caused by too small orifice or high gas pressure

Sensor cools off

Blue / Steady Flame

Ideal condition

Post aerated pilot uses primary and secondary air but has no?

Mixing tube

What’s the name of the electromagnetic device used as a load in a safety circuit called?

Power Unit

T/C reads 26mV open and 6mV closed, what does it mean?

Replace T/C

T/C reads 16mV open and 16mV closed, what does it meant?

Check Power uni

t and check T/C

If thermopile wire exceeds 80ft, what system should you considr?

24V system. thermopile will have voltage loss

What is the thermopile test called similar to a drop out test in a t/c

Pull in voltage test

What test is done on thermopile to test proper ignition off the main burners at a low pilot flame condition

Effective Ignition Test