hi patpin,

The gain of this demo circuit is set to give a -/+1Vout range for a Vhall signal of -10mV thru +10mV.

E

Indeed 1mV/Amp.

 

hi,
A common way is to use say a TL431 reference driving a OPA, the output of the OPA would be connected to the Vref pin.
If you configure the TL431 ref source to be adjustable, you can set the Vref to suit your application.
E

I have followed yr diagram with the 2 100K R's. It influences the output of the Clamp-on current meter (=input of the 623). It becomes -5,2mV without 1A current running throught ferrite and -5.7mV with 1 Amp . But the output of the AD623 remains at 1.61V. I tried to augment the gain of IC1a; The difference between measuring 1 Amp and not, became larger (1.2mV) but still no change in output of AD623

 

Which post number has that diagram with 100K?
E

 

hi patpin,
Using your Hall device I would suggest this option as being an improvement over your original circuit.

Its uses an OPA to give a Virtual Gnd [vg ], the 2.5vg is based on the Hall device datasheet typical value of 2.5V quiescent output, which has a possible Q range of 2.25v thru 2.75v.
It would require that you set the Vg voltage to suit, using the 1k pot.
The gain of this demo circuit is set to give a -/+1Vout range for a Vhall signal of -10mV thru +10mV.
As I do not know the coupling coefficient of your Clamp/Hall I have assumed -/+10mV swing for -/+10Amps.

Your DVM [ connected between Vout and Vg] would show a range of -1v thru +1v for -/+10Amps, for the sim circuit.

E

Hi Eric, Before trying to realise the diagram you designed (many thanks for it) , a few questions.
1/ what about measuring negative currents through ferrite; My guess: no problem!?
2/ The ultimate goal is to be able to see the current changes (at max.+-1000HZ)(of injectors)(+-3 Amp) with a bitscope BS05.
The ground of the bitscope will be the car battery MINUS. The triggering signal on the A channel of the scope will be a signal coming from the firing of a cylinder and be measured with a capacitive pick up probe referenced to the ground followed by a 10/1 reduction and led to the bitscope.https://www.dfad.com.au/links/THE SECRET WORLD OF PROBES OCt09.pdf
This bitscope A channel should be also the trigger for channel B where I 'll measure current changes with the instrument described here. The virtual ground you propose will be different from the car battery MINUS . I can connect only 1 ground to the bitscope... Is there a problem here... and how can one resolve that?

 

Which post number has that diagram with 100K?
E

#36 (91K)

 

Hi,
Post 36 is not my circuit.
I will look at the injector requirement, let you know.

E

 

hi patpin,

Your DVM [ connected between Vout and Vg] would show a range of -1v thru +1v for -/+10Amps, for the sim circuit.

E

Hi ERIC, been looking at yr last sim. in the A03 sim included in post #40. Can I assume that "U5" in is a typo?

 

#36 (91K)

yes 91k...

 

Can I assume that "U5" in

hi,
U5 is the circuit Ident for the 1K pot, the 'wiper= 0.58' value, indicates that the pot has been rotated 58% of its travel.
It sets the voltage of the virtual ground, which is typically 5v/2.

I assume that as you show a 9V voltage supply, that the project is powered from a 9v battery.??
If so, the project is 'floating', that means that your Scope 0V common Input can be connected to Vg [ vehicle chassis neg] and the Scope signal Input connected to Vout of the IA.

Are you requiring to view a sharp 1000Hz square wave current signal on the Scope or just a 'rough' 1000Hz signal.??

E

EDIT:
This image shows how the '9v battery powered floating' circuit would connected to the vehicle battery/Scope

 

hi,
U5 is the circuit Ident for the 1K pot, the 'wiper= 0.58' value, indicates that the pot has been rotated 58% of its travel.
It sets the voltage of the virtual ground, which is typically 5v/2.

I assume that as you show a 9V voltage supply, that the project is powered from a 9v battery.??
If so, the project is 'floating', that means that your Scope 0V common Input can be connected to Vg [ vehicle chassis neg] and the Scope signal Input connected to Vout of the IA.

Are you requiring to view a sharp 1000Hz square wave current signal on the Scope or just a 'rough' 1000Hz signal.??

E

EDIT:
This image shows how the '9v battery powered floating' circuit would connected to the vehicle battery/Scope

Thanks again for the sim
Example of the scope of the current througt injector. It is important to see the little pintle hub (black arrow).
Yes the current probe should function independently on the 9V batt,. The bitscope gets its power from the USB. The signal from the capacitive pickup of the firing of a cylinder (High tension 3KV; Capacitive pickup ratio 100:1--> 30V; after that a scope probe 10:1 ---> 3V ; This goes to Chan A of Bitscope (where I can study the shape of the HV wave) and also serves as the trigger for the scope for CHAN B for the injectors (using the current probe).
- The thing I worry about is the connection of the grounds of scope, capacitive pick up probe for High Tension and the current probe discussed here.
- And of coarse the problem of connection of bitscope ground to USB port...
- I also worry what could happen if a spark finds that the path to the pickup probe (around the exterior of the sparkplug wire) is an easier way to go... Is an optocoupler advised or isn't that a sufficient isolation either

PS: the bitscope specs:http://www.bitscope.com/product/BS05/?p=specs

 

hi patpin,
Using your Hall device I would suggest this option as being an improvement over your original circuit.

Its uses an OPA to give a Virtual Gnd [vg ], the 2.5vg is based on the Hall device datasheet typical value of 2.5V quiescent output, which has a possible Q range of 2.25v thru 2.75v.
It would require that you set the Vg voltage to suit, using the 1k pot.
The gain of this demo circuit is set to give a -/+1Vout range for a Vhall signal of -10mV thru +10mV.
As I do not know the coupling coefficient of your Clamp/Hall I have assumed -/+10mV swing for -/+10Amps.

Your DVM [ connected between Vout and Vg] would show a range of -1v thru +1v for -/+10Amps, for the sim circuit.

E

Hi Eric , I realised yr diagram in post #40. It is functioning: For a Hall change of -1mV the output referenced to Vg changes from 0 to -1.74 VOLT!. which is a little bit to much gain. What is the best way to reduce it to about 100?

 

What is the best way to reduce it to about 100?

The usual way would be to make the 'gain' resistor, presently a 1k01, a variable pot. [pins# 1 and 8 of the AD623]

ie: a fixed 1K resistor in series with an adjustable 5K pot, this would give a gain control of 15 thru to 100 times.

E

 

The usual way would be to make the 'gain' resistor, presently a 1k01, a variable pot. [pins# 1 and 8 of the AD623]

ie: a fixed 1K resistor in series with an adjustable 5K pot, this would give a gain control of 15 thru to 100 times.

E

Indeed I also checked this table and expected gain 100 instead of 1700 as measured now, but this is probably due to the BC547. Anyway I 'll put a potmeter and the probl will be solved. Thanks.
The other points in #50 are much more important. I would be very pleased if U could look at it.

 

hi,
The DVM should be connected between Vout and Vg, not Vout and 0V

I would say that as the BSS is powered from the USB, the 0V side of the Input signal of the BSS is connected also to 0V, you could check this by using a Ohm meter [ with the BSS disconnected from the USB port.]

It should be possible to see the injector waveform 'spike' on BSS Scope.

The EHT cable 'Sync' pick up could be problem, you could consider a Opto-coupler with output clamping diodes before the BSS sync input.

Do you have details of the capacitive EHT pick up.?

E

 

hi,
The DVM should be connected between Vout and Vg, not Vout and 0V

I would say that as the BSS is powered from the USB, the 0V side of the Input signal of the BSS is connected also to 0V, you could check this by using a Ohm meter [ with the BSS disconnected from the USB port.]

It should be possible to see the injector waveform 'spike' on BSS Scope.

The EHT cable 'Sync' pick up could be problem, you could consider a Opto-coupler with output clamping diodes before the BSS sync input.

Do you have details of the capacitive EHT pick up.?

E

Indeed I measured between Vo and Vg
Capacit P.U. looks like
and consists of a longitudinally split metal tube of 8mm of a few cm long glued on a clothes peg. in order to "capture" the signal by putting it on the sparkplug cable.
Found complete article in a pdf:
http://www.lotuselan.net/forums/download/file.php?id=9946

 

hi,


The EHT cable 'Sync' pick up could be problem, you could consider a Opto-coupler with output clamping diodes before the BSS sync input.

Do you mean one or more varistors? Where do you put the opto-coupler protection considering the given diagram of the High Voltage pickup probe; which optocoupler would you use and what kind of varistors: for what voltage and how many joules? Sorry ... there are a lot of questions again...

 

hi,
I would say that as the BSS is powered from the USB, the 0V side of the Input signal of the BSS is connected also to 0V, you could check this by using a Ohm meter [ with the BSS disconnected from the USB port.]
E

i'am afraid I don't understand what you exactly mean by that.

 

hi,
Looking at your injector current waveform, it should be possible to Sync the BSS Scope to the Low going leading edge of the current pulse, so that you can observe the back emf 'spike' from the injector coil.

As well as the injector current waveform do you want to view the distributor contact waveforms.?

I will post a sketch of the BSS/USB power connections.

 

hi,


As well as the injector current waveform do you want to view the distributor contact waveforms.?

In my case its also a hall sensor. Could be interesting to see the output of it with the scope in case there is no firing at all.

 

Hi
I have just built the original circuit I posted earlier, it works fine for a Hall input range of +/-10mV [ superimposed on a +2.5v DC level, the Hall Q point]

Measuring between Vout and Vg it gives a voltage of +/-1Volt which is 100mVout/1Amp, I would suggest setting your Scope to 100mV scaling.

Note if your 100K's connected to the 1K U5 pot are not high tolerance, say 0.1%, you may have to use a 10K pot for U5.
With the Hall device connected and no clamp current, adjust U5 to give 0V between Vout and Vg.

Are you trying to test the injectors for 'wear, sticky or dirty'?

I guess you know that spike on the waveform is due to the back emf produced by the injector coil inductance, when the driving current is switched off.?

E