Lo Z mode on DMM meters

[Ericwatson]

What is the Lo Z mode on fluke DMM meters used for?

Is it better to test transistors in a Lo Z mode because it loads the transistors junctions to measure leakage?

Technicians have told me to use older Lo Z analog meters to measure a battery because the Lo Z input circuit loads the battery. What other kinds of components would be better to set with Lo Z or want to add a circuit load during measurement?

Can I take a new Fluke DMM meter that has a 10 meg impedance and put a 10K or 1K in parallel across the red and black jacks on my fluke meter to make it a Lo Z meter?

Older analog meters loaded down the circuit when measuring voltages and resistances. How do Electronic technicians back in the 60's make voltage and resistance measurements when the meters was loading it down?

 

[ads-ee]

The first thing you need to do is learn how to use Google.

2nd link provided by google was the following (on Fluke's website):


You're lucky I even looked this up (primarily because I wasn't familiar with LoZ).

 

[Ericwatson]

yes I have read this

What I'm confused about what components or circuits for electronics would I use it for. I know it's for electricians and wiring up houses. I need more examples of testing components and what circuits would I use the Lo Z as for electronic technicians and troubleshooting boards using the Lo Z mode

Older Analog meters loaded down circuits and components, how did electronic technicians measure resistances and voltages since the circuit was loading down from the meter which changed the resistance and voltage measurements. So how did electronic technicians know if the stage was good or not because the meter was loading it down and changing the resistance and voltage values from loading.

 

[Audioguru]

My 9V battery tester has a 850 ohm load (10.6mA on a new battery.
It has a load of 10 ohms for an AA battery cell (150mA or 160mA) on a new battery.

 

[Ericwatson]

but how did electronic technicians know if the stage was good or not good because analog meters loaded down the circuit. It seems it gave false AC and DC voltage measurements when testing stages in-circuit. So did electronic technicians have to use a calculator and formulas when doing measurements since the older meters loaded the circuit down?

 

[Audioguru]

A technician would measure voltages on a good circuit then see if the bad circuit voltages are different. Then the meter loading the circuit does not matter.
Sometimes the service manual shows voltages that were measured with a meter of that time.

 

[Ericwatson]

If the technician didn't have a known good board to compare to or the schematic or service manual that had the voltages. How would a technician know if those AC and DC voltages were good or not because of the meter loading issues?

Would they have to use the parallel resistance equivalent circuit formula?
Or is there meter loading formulas that were used

It says in analog meters that using RX1 to test transistors will damaged the transistors junctions because RX1 has to much test current. I'm guessing different analog meters RX1 has more or less test currernt depending on the brand and model.

 

[D.A.(Tony)Stewart]

If you are measuring DC and have long wires and are concerned about noise then choose a Cap that suppresses the noise. Choose ESR of cap to suit environment.

This will be much lower Z than using R=1k for DC,

 

[chuckey]

I first started "mending" radio and TV sets in about 1959 with a 1000 ohms per volt multimeter. The fact is that in those days the DC voltages were not critical, if a valve had 15V on its screen grid then there was a problem if it had more then 100V then there was no problem unless it was a power output valve then you were looking for more then 250V. There were no DC coupled amplifiers and there was no need to measure the .3-.7V forward bias on a transistor. Life was much simpler then !
Frank

 

[D.A.(Tony)Stewart]

I started with a 50kΩ/V analog meters in 1969, a decade later and I still use it on occasions 45 yrs later.

After I read every CMOS Design & Application Note upon graduation, I started designing digital Doppler Radios with analog front ends.
I learn how to calibrate my fingers in pF to nF and GΩ to kΩ.

... so I could quickly see problem areas in a design with finger bias. You can't easily do that in valves with >100V bias
.. so life was much simpler then.. until I discovered ESD can kill TTL too.

 

[BradtheRad]

It says in analog meters that using RX1 to test transistors will damaged the transistors junctions because RX1 has to much test current. I'm guessing different analog meters RX1 has more or less test currernt depending on the brand and model.

My analog meter can push 60mA in the Rx1 setting. It is due to the 1.5V battery inside. This is able to ruin some components (such as a transistor bias junction).

Therefore I start measuring at a higher ohm range. If I don't get a sensible reading, then I switch to a lower range.

 

[Ericwatson]

My analog meter can push 60mA in the Rx1 setting. It is due to the 1.5V battery inside. This is able to ruin some components (such as a transistor bias junction)

What is the maximum current can a transistor handle without damaging it's junctions?

Analog Test voltage and Test current:
RX1 test voltage is 1.5 volts at 125mA or 250mA
RX100 test voltage is 1.5 volts at 1.25mA or 2.5mA
RX1K test voltage is 1.5 volts at 250uA
RX10K test voltage is 9 volts at 75uA or 125uA
DC volts impedance is 20K
AC volts impedance is 5K

I have seen different Analog meter sensitivity input Impedance:
1K input impedance
2K input impedance
20K input impedance
30K input impedance

I know using a FET VOM or Tube VOM would not load a circuit when measuring a voltage in circuit.

I read on google that most techs use an analog meter to measure fluctuations in circuits and to measure the peak because of the response of the needle is very fast. What circuits would I want to measure the fluctuations and peak of what?

An Analog meters can measure an AC frequency up to 2K. Technicians would use an Analog low impedance meter for high frequency oscillator circuits it says on google i read somewhere.

 

[Audioguru]

Why blow up a low current transistor junction with a high current when a safe low current will test it?
An analog meter with a moving needle is not fast and will probably have overshoot. Use an oscilloscope to see accurate peak voltage swings.
Also use an oscilloscope to see a high frequency oscillator output.