Jaycar panel meter, QP5585

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I recently ordered the following panel meter from a Jaycar stockist:
 http://www.jaycar.com.au/productView.asp?ID3D%QP5585

The catalogue describes it as "not just a digital display, but a fully
functional high impedance digital panel meter that only requires power
to operate. It will measure voltages from 200mV to 500VDC (jumper
selectable) and has a maximum count of 1999".

Based on the above description it would be reasonable to expect that
the meter would have 5 decadic ranges, namely 200mV, 2V, 20V, 200V,
and 500V (2000V), as do all (?) other panel meters and multimeters.
But, inexplicably, this meter does not have a 2V range. There doesn't
seem to be any logical reason for this because the ranges are selected
by a single potential divider - an additional range would have
required only an extra resistor and an extra couple of PCB pads.

You can guess which voltage range my application requires. :-(

- Franc Zabkar
--20%
Please remove one 'i' from my address when replying by email.

Re: Jaycar panel meter, QP5585



I recently ordered the following panel meter from a Jaycar stockist:
 http://www.jaycar.com.au/productView.asp?ID=QP5585

The catalogue describes it as "not just a digital display, but a fully
functional high impedance digital panel meter that only requires power
to operate. It will measure voltages from 200mV to 500VDC (jumper
selectable) and has a maximum count of 1999".

Based on the above description it would be reasonable to expect that
the meter would have 5 decadic ranges, namely 200mV, 2V, 20V, 200V,
and 500V (2000V), as do all (?) other panel meters and multimeters.
But, inexplicably, this meter does not have a 2V range. There doesn't
seem to be any logical reason for this because the ranges are selected
by a single potential divider - an additional range would have
required only an extra resistor and an extra couple of PCB pads.

You can guess which voltage range my application requires. :-(

- Franc Zabkar
-------------------------------


Surely you can use the 200mV range and provide your own multiplier resistor,
or possibly swap one of the ones already there?


MrT.



Re: Jaycar panel meter, QP5585


keyboard and composed:

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I had resigned myself to modifying the 20V range (the 200mV range is a
direct input to the A/D chip), but at the cost of precision. The
existing resistors have special values.

In any case my post was intended as a complaint about the product as
well as a warning to others.

- Franc Zabkar
--20%
Please remove one 'i' from my address when replying by email.

Re: Jaycar panel meter, QP5585



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Excuse my ignorance (it's been a while since I did much analogue
electronics), but can't you just use a 1K/10K divider on the 20V setting?
This doesn't need any special values, just low tolerance resistors.

- Gadget

Re: Jaycar panel meter, QP5585



. . .
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Depending on which way you connect them you would have 220V or 22V
giving a reading of 20V.




Andy Wood
snipped-for-privacy@trap.ozemail.com.au

Re: Jaycar panel meter, QP5585



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Firstly he wants to measure 2V, not 200V.
Secondly measuring anything with an 11k ohm input impedance is asking for
loading errors, even assuming the DVM had an infinite input impedance itself
(and it doesn't).

MrT.



Re: Jaycar panel meter, QP5585



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Ah, the brain to keyboard police are out in force :)

My point is that is the bottom range bypasses all the 'special' resistor
values then providing your own divider with the correct ratio will do
exactly the same thing, avoiding rewiring the existing ranges. If the
existing 2V one uses 100M and 1M then replace it with either 10M and 1M, a
100M pot, or 2x33M/33M.

As Franc 'needs' a 2V solution there's a good chance he knows exactly what
the impedance can be and can avoid the loading issues.

Gadget

Re: Jaycar panel meter, QP5585


On Wed, 15 Nov 2006 22:17:19 +1100, Jason Sobell <jason_sobell.net>
put finger to keyboard and composed:

Quoted text here. Click to load it

This is the existing divider network:

 Vin o----|----o  o---| 200mV
      Ra 9M9          |
          |----o  o---| 20V
      Rb 90K          |---------> to A/D chip ( >100Mohm )
          |----o  o---| 200V
      Rc 9K           |
          |----o  o---| 500V (2kV)
      Rd 1K
         _|_
          3D%

Clearly the input impedance is 10Mohm, yet the panel meter's specs
state ">100Mohm".

If the meter had been designed "properly", then the divider would have
looked like this:

 Vin o----|----o  o---| 200mV
      Ra 9M           |
          |----o  o---| 2V
      Rb 900K         |
          |----o  o---| 20V
      Rc 90K          |---------> to A/D chip ( >100Mohm )
          |----o  o---| 200V
      Rd 9K           |
          |----o  o---| 500V (2kV)
      Re 1K
         _|_
          3D%

46%ortunately my application only requires a 2V range, so I'll just add
an extra 1Mohm to Rb making it 1090K. The panel meter has a trimpot
which will hopefully account for any tolerances.

- Franc Zabkar
--20%
Please remove one 'i' from my address when replying by email.

Re: Jaycar panel meter, QP5585


On Thu, 16 Nov 2006 08:21:40 +1100, Franc Zabkar

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If you are not bothered about the loading then just bridge the 500v
link and put a suitable (lowish value) resistor across the 200mV link.

Alternatively select the 200mV range and put an external resistor
(approx 100M) on the input to increase the range.  

Or select the 200mV range and put an external voltage divider on the
input.

Lots of possibilities!

Alan

--
Sell your surplus electronic components at
http://ozcomponents.com
We've slightly trimmed the long signature. Click to see the full one.
Re: Jaycar panel meter, QP5585



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how to get a 2V range:

  Vin o----|----o  o---| 200mV
       Ra 9M9   |      |
           |----o  o---| 20V
       Rb 90K          |---------> to A/D chip ( >100Mohm )
           |----o--o---| 200V
       Rc 9K           |
           |----o  o---| 500V (2kV)
       Rd 1K
          _|_
           =

Bye.
   Jasen

Re: Jaycar panel meter, QP5585



"Jason Sobell" <jason_sobell.net> wrote in message
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setting?
Quoted text here. Click to load it
for
itself


At least the first time you had the grace to excuse your ignorance :-)

MrT.



Re: Jaycar panel meter, QP5585



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Sorry, it's always nice to see a "actually, I think you meant this..."
rather than a "you idiot..." style response. There are many ways to define
grace.

Still, it's nice to see Alan giving a constructive and helpful response!
Thanks Alan :)

Cheers,
 Gadget

Re: Jaycar panel meter, QP5585


Frank,

One of those meters (can not remember if it this one) had an error in
description. Input signal is differential, not a common ground!

Rudolf

I recently ordered the following panel meter from a Jaycar stockist:
 http://www.jaycar.com.au/productView.asp?ID=QP5585

The catalogue describes it as "not just a digital display, but a fully
functional high impedance digital panel meter that only requires power
to operate. It will measure voltages from 200mV to 500VDC (jumper
selectable) and has a maximum count of 1999".

Based on the above description it would be reasonable to expect that
the meter would have 5 decadic ranges, namely 200mV, 2V, 20V, 200V,
and 500V (2000V), as do all (?) other panel meters and multimeters.
But, inexplicably, this meter does not have a 2V range. There doesn't
seem to be any logical reason for this because the ranges are selected
by a single potential divider - an additional range would have
required only an extra resistor and an extra couple of PCB pads.

You can guess which voltage range my application requires. :-(

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.



Re: Jaycar panel meter, QP5585


On Thu, 16 Nov 2006 11:56:50 +1100, "Rudolf"

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This is the "B" version which has a common ground. The "A" version is
differential. Thanks anyway.

Quoted text here. Click to load it

- Franc Zabkar
--20%
Please remove one 'i' from my address when replying by email.

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