Icl7106

[nitE]

im trying to built a voltmeter which measure up to 200V from ICL7106.. from what i read.. the panelmeter from intersil app note AN023.. it only measure to 200mV and i had to do something to its Vref and the voltage divider.. from my understanding to measure up to 200V, the Vref had to be 100V? if so how do i voltage divide to get 100V because its V+ is only 9V.. do i use a different voltage source and if so will the IC spoilt..?

best regard
nitE

 

[ericgibbs]

im trying to built a voltmeter which measure up to 200V from ICL7106.. from what i read.. the panelmeter from intersil app note AN023.. it only measure to 200mV and i had to do something to its Vref and the voltage divider.. from my understanding to measure up to 200V, the Vref had to be 100V? if so how do i voltage divide to get 100V because its V+ is only 9V.. do i use a different voltage source and if so will the IC spoilt..?

best regard
nitE

hi,
Use the basic range of 200mV and add a resistive potential divider on the High and Low inputs.
Use a divider ratio that will give 200mV at its junction for 200V input at the 'top' of the divider.
OK.?

 

[nitE]

i think i get it now.. many thanks

nitE

 

[ericgibbs]

i think i get it now.. many thanks

nitE

Is this the 50MΩ application.???

 

[nitE]

ya.. so does it work..?

nitE

 

[ericgibbs]

ya.. so does it work..?

nitE

The divider will work, but you were concerned about loading the voltage source.

Say you made the 'low' end resistor 10K, that would mean a current of about 20µ amps, so to drop 199.8V across the 'top' resistor, I make it 9.99MΩ.

Is that going to load the source.???

 

[nitE]

The divider will work, but you were concerned about loading the voltage source.

Say you made the 'low' end resistor 10K, that would mean a current of about 20µ amps, so to drop 199.8V across the 'top' resistor, I make it 9.99MΩ.

Is that going to load the source.???

hmm.. i believe to get max 200V on this 7106, i will need 10KΩ to 9.99MΩ but this isn't going to be good enuff to measure the 50MΩ voltage divider as it will cut down the resistance so in ratio of 10kΩ:10MΩ, i increase it to 1MΩ:1GΩ but im worried about using such a large resistance.. will it cause any problem to the circuit..?

nitE

 

[ericgibbs]

hmm.. i believe to get max 200V on this 7106, i will need 10KΩ to 9.99MΩ but this isn't going to be good enuff to measure the 50MΩ voltage divider as it will cut down the resistance so in ratio of 10kΩ:10MΩ, i increase it to 1MΩ:1GΩ but im worried about using such a large resistance.. will it cause any problem to the circuit..?

nitE

hi,
IMO the current flowing in the divider of 1M/1G is going to be so small that the slightest change in temperature or resistance will make the reading unreliable.
Also I would check the 7106 input pin current/resistance specification.

Can you give some details of the 200Vdc supply you are trying to measure.?

 

[nitE]

im trying to measure the voltage of unknown insulation resistance as compare to a 50MΩ with a supply of 200V.. so if the voltage is higher than 100V i can determine that the unknown resistance i higher than 50MΩ..

 

[ericgibbs]

im trying to measure the voltage of unknown insulation resistance as compare to a 50MΩ with a supply of 200V.. so if the voltage is higher than 100V i can determine that the unknown resistance i higher than 50MΩ..

If I follow correctly, you want to measure the insulation resistance of a 'device' using 200Vdc,
in order to test that the insulation resistance is greater than 50MΩ.??

Is that correct.?

 

[nitE]

If I follow correctly, you want to measure the insulation resistance of a 'device' using 200Vdc,
in order to test that the insulation resistance is greater than 50MΩ.??

Is that correct.?

yes.. is the method feasible..?

 

[nitE]

i was daydreaming.. playing with calculator.. and suddenly my mind just think out a way that i can still maintain the 10MΩ/10kΩ voltage divider and still can measure insulation resistance and that is to change the 50MΩ intially i wanted to use to measure the insulation resistance to just abt 8.5MΩ (the total parallel resistance of the 10MΩ/10kΩ and insulation resistance).. so i tested it out on the breadboard.. something puzzled me is that when i connect 20V across the whole circuit the top part (8.5MΩ) measure abt 7V and the bottom part( the insulation resistance part) also measure abt 7V but it doesn't telly up to 20V does it? so where do the rest of the voltage gone..?