TP4000ZC is not read correctry paralell resistors

[jhcl21]

I got tekPower TP4000ZC for my 1st DMM.
I bought this DMM because of the price and EVV's video review is good.
I'm very happy on this mater except bellow problem.

I made a simple circuit on a breadboard.
6v power, two 1k ohm resistors in parallel, that's it.
http://d3j5vwomefv46c.cloudfront.net/photos/large/776678877.jpg
(note: I used Metal film Resistors)

and Try measure current.
This DMM read 5.57mA which is should be near 12mA.
Actually, I used $15 analog tester , it read 12mA which is correct.

Even If I took off one resistors it is not changed.
so apparently This DMM only measuring one resistor ,even it is in paralell.

I have very disappointed on this and packed to return.
But before going forward,  I would like to know if I missed something.

Please help me.

thank you

[Nermash]

Maybe you measured current in only one branch? Try measuring current with only battery and one 1k resistor. Verify first that both resistors have 1k ohm resistance. Too early in the morning for logic  Since you measured 12 mA both resistor should be OK.

[jhcl21]

Thank you for reply.
I appreciate.


When I measure only battery(6v) and one 1k resistor , It is 5.57mA that is correct.
I measured both resistors and result is same.
I used them in the series for just make sure and it was read correctly (about 3mA) on  TP4000ZC, so I think both resistors and TP4000ZC are nothing wrong on this.


On the breadboard I made this connection.
d3j5vwomefv46c.cloudfront.net/photos/large/776691529.jpg
I gather output from parallel link of resistor to one.

Also I gather both resistors by alligator clips and connect it to the battery and DMM.
Both(breadboard and Arrigator clips) result are same.

TP4000ZC read only one resistor result (5.57mA)not parallel value.
My Analog tester (GMT-312) reads 12mA.

[amyk]

Since you seem to have two multimeters, measure the voltage across the resistors with the DMM in circuit, then measure the voltage across the DMM's terminals.

[alanb]

It would also be interesting to put both meters in series and see if they still show different currents. If they do then one of them must be suspect.

[jhcl21]

Thank you for the instruction.
I tested both.?


>amyk
I placed TP4000ZC in the circuit.(in the series, set mA range)
Then I used GMT-312 for measuring.

The result is below
Across resistors: zero
Across TP4000ZC: 6v
Entire circuit : 6v

The voltage across the resistors is zero.
GMT-312 doesn't read any value.
I also measure voltage across TP4000ZC in circuit it is 6v.

For the test , I swapped DMMs, GMT-312 in the circuit then measuring by TP4000ZC.
Across resistors : 6.13V
Across GMT-312: 184mV
Entire circuit: 6.34v


> alanb
I connect TP4000ZC and GMT-312 in the series.
(battery positive > resistors > TP4000ZC > GMT-312 > battery negative)

TP4000ZC read 5.52mA,
(Current is  little less than last time, because I used this battery for an other project).
GMT-312 doesn't read anything. The needle doesn't react.

I swapped order GMT-312 and TP4000ZC.
(battery positive > resistors > GMT-312 >TP4000ZC > battery negative)
It is the same result
TP4000ZC read 5.52mA, GMT-312 doesn't read anything.

I appreciate to the advices to get clear the situation.
I guess TP4000ZC has bigger resistance in this circuit.
Is that why it is not reading correctly.
I am afraid of if Any DMM will behave like this.

Is it correct?

[c4757p]

Is that why it is not reading correctly.
I am afraid of if Any DMM will behave like this.

Is it correct?

Yes, most DMMs have a fairly high measuring resistance. You'd have to use another method to measure the current in this circuit. Ideally, just measure the voltage across the resistor in circuit, then remove the resistor and measure its value, then compute the current using Ohm's law.

In practice it's not usually as much of a problem as it seems, though for when it is, there's always Dave's µCurrent. The voltage error is at most 0.021V on the mA range and 0.01V on the lower ranges.

[jhcl21]

Yes, most DMMs have a fairly high measuring resistance. You'd have to use another method to measure the current in this circuit. Ideally, just measure the voltage across the resistor in circuit, then remove the resistor and measure its value, then compute the current using Ohm's law.

In practice it's not usually as much of a problem as it seems, though for when it is, there's always Dave's µCurrent. The voltage error is at most 0.021V on the mA range and 0.01V on the lower ranges.

Thank you for reply.
I understand what happened on this  TP4000ZC.

I'm learning from the book "Make:Electronics", and it was one of the excise.
In this book looks no problem using DMM on this circuit.
I think I chose wrong one.

I will return TP4000ZC and will get other one to try.
I know there is no guarantee, but want try anyway.

Also thank you for info about µCurrent  it is good to know.
 

[iloveelectronics]

I set up the exact same circuit and measured the current with my Digitek DT-4000ZC, which is essentially the same meter as the Tekpower TP4000ZC. It measured 12mA, no problem at all. I think you might have got a faulty meter.

[jhcl21]

I set up the exact same circuit and measured the current with my Digitek DT-4000ZC, which is essentially the same meter as the Tekpower TP4000ZC. It measured 12mA, no problem at all. I think you might have got a faulty meter.

Thank you very much for testing.
It is created cleared now,  I will get new meter!

[c4757p]

That's interesting. I can't find any detailed images, but the one picture I found of the inside of this meter clearly shows multiple trimpots. You'd think something like this would be noticed during adjustment... 

[jhcl21]

That's interesting. I can't find any detailed images, but the one picture I found of the inside of this meter clearly shows multiple trimpots. You'd think something like this would be noticed during adjustment... 

Thank you for further?information.
I found some pictures about inside.
http://sigrok.org/wiki/TekPower_TP4000ZC
Possibly This DMM can be adjusted by the trimpots?
but It is too advanced for me at this time.
But good to know.
Thank you !

[jhcl21]

I got my UNI-T, today.
Its read perfect!!

https://pbs.twimg.com/media/BMJBVqxCUAAY1Sf.jpg:large

[iloveelectronics]

That's interesting. I can't find any detailed images, but the one picture I found of the inside of this meter clearly shows multiple trimpots. You'd think something like this would be noticed during adjustment... 

Thank you for further?information.
I found some pictures about inside.
http://sigrok.org/wiki/TekPower_TP4000ZC
Possibly This DMM can be adjusted by the trimpots?
but It is too advanced for me at this time.
But good to know.
Thank you !

For Digitek DT-4000ZC (which measures temperature in Celcius), the 4 trim pots from top to bottom are for the following adjustments (in this order): DCV, ACV, 100 degree C temperature, 0 degree C tempearature.

[amyk]

You can use one DMM in ohms mode to measure the resistance of the shunt of the other in current mode.