Oscillator design

Thread Starter

irsarasheed

Joined Dec 24, 2019
31
I need to produce oscillations using 2P 3S transformer coupled oscillator. CI have attached the circuit diagram also. I have tried to implement it in Multisim many times, but I am unable to get oscillations. Can anyone help please? I really need to complete this task.
 

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Danko

Joined Nov 22, 2017
1,005
I need to produce oscillations using 2P 3S transformer coupled oscillator. CI have attached the circuit diagram also. I have tried to implement it in Multisim many times, but I am unable to get oscillations. Can anyone help please? I really need to complete this task.
So, it produces oscillations:
1582986585648.png
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1582986693827.png

That is great, I am really thankful for your kind response. I'll implement it in LTSPICE, but I want to use it in another configuration, in which one of the primary winding of transformer is feedback winding. I am attaching the labelled diagram with it. The windings on the secondary side make the L for the LC tank. The C for the LC tank is also on the secondary side as shown in figure. The oscillator uses 2 Primary, 3 secondary transformer. This oscillator is to be used in Pressure transmitter circuit shown in second figure. Please help in producing oscillations of 30Vp-p and 32kHz. Second figure also specifies values for the components. I'll really appreciate your help.
Use 2nd example from this post.
To L1 (primary) and L2 (feedback) windings add L3 with capacitor in parallel (LC tank) and two secondary windings: L4 and L5.
Your circuit will oscillate, and your problem will resolved.
 
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Thread Starter

irsarasheed

Joined Dec 24, 2019
31
That is great, I am really thankful for your kind response. I'll implement it in LTSPICE, but I want to use it in another configuration, in which one of the primary winding of transformer is feedback winding. I am attaching the labelled diagram with it. The windings on the secondary side make the L for the LC tank. The C for the LC tank is also on the secondary side as shown in figure. The oscillator uses 2 Primary, 3 secondary transformer. This oscillator is to be used in Pressure transmitter circuit shown in second figure. Please help in producing oscillations of 30Vp-p and 32kHz. Second figure also specifies values for the components. I'll really appreciate your help.
 

Attachments

Thread Starter

irsarasheed

Joined Dec 24, 2019
31
View attachment 200243
==================================================================================================
View attachment 200244
That is great, I am really thankful for your kind response. I'll implement it in LTSPICE, but I want to use it in another configuration, in which one of the primary winding of transformer is feedback winding. I am attaching the labelled diagram with it. The windings on the secondary side make the L for the LC tank. The C for the LC tank is also on the secondary side as shown in figure. The oscillator uses 2 Primary, 3 secondary transformer. This oscillator is to be used in Pressure transmitter circuit shown in second figure. Please help in producing oscillations of 30Vp-p and 32kHz. Second figure also specifies values for the components. I'll really appreciate your help.
 

Attachments

Thread Starter

irsarasheed

Joined Dec 24, 2019
31
Sir I have attached circuit of pressure transmitter implemented in LTSPICE. It is the same circuit of which oscillator is a part. I could not find trimmer capacitor in LTSPICE. But for checking the working, I have used combination of capacitors. When circuit is working properly, the variation in Trimmer/Variable capacitor should produce a current of 4 to 20mA through the output resistance R22 in LTSPICE circuit. I am unable to make the circuit in working conditions. I have tried in MULTISIM also. But I didn't succeed. Can you please help me ? Please guide me how can I remove error? Even oscillations are not produced in the complete circuit. I really need your guidance/help. I can provide you more information which you require. Please help me , I have been working for so long but could not find the solution.
 

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Thread Starter

irsarasheed

Joined Dec 24, 2019
31
Sir I have attached circuit of pressure transmitter implemented in LTSPICE. It is the same circuit of which oscillator is a part. I could not find trimmer capacitor in LTSPICE. But for checking the working, I have used combination of capacitors. When circuit is working properly, the variation in Trimmer/Variable capacitor should produce a current of 4 to 20mA through the output resistance R22 in LTSPICE circuit. I am unable to make the circuit in working conditions. I have tried in MULTISIM also. But I didn't succeed. Can you please help me ? Please guide me how can I remove error? Even oscillations are not produced in the complete circuit. I really need your guidance/help. I can provide you more information which you require. Please help me , I have been working for so long but could not find the solution.
I am re sending the circuit implemented in LT SPICE after making small corrections.
 

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Thread Starter

irsarasheed

Joined Dec 24, 2019
31
Thank you so much Sir, you are a great person. I am working on it. If I face problem, I'll inform you. Your help is well-appreciated.
 

Thread Starter

irsarasheed

Joined Dec 24, 2019
31
32 kHz, 32Vp-p on windings L1, L2, L3 :
View attachment 200542

Diode D15 prevents transition B-E of Q1 from breakdown:
View attachment 200544

Sir, you are a great person and you have helped me a lot. But I am Still facing problems. According to the circuit operation, the output current through the load resistance should change between 4 to 20mA as we vary the value of sensing element capacitance by very small amount. Some of my question are:
  • Why sometimes the oscillations become like this as shown in figure.
  • The Zener diode to be used in 1N4571 and 1N4761, I could not find them in LTSPICE, and tried to use closest match. Is my selection, right?
  • I can make variable capacitor by using .step param. Is there any other option? Is the sensing element connected in the right way?
I am also attaching LTSPICE circuit file, a word document which explains the working of this transmitter circuit. Please help me in making this circuit operational. I really need your help. Waiting for your affectionate and kind response.1583414003241.png
1583413570035.png
 

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Thread Starter

irsarasheed

Joined Dec 24, 2019
31
32 kHz, 32Vp-p on windings L1, L2, L3 :
View attachment 200542

Diode D15 prevents transition B-E of Q1 from breakdown:
View attachment 200544
When I apply .step parameter for the sensing element capacitance, I get variation in Pulse Width as shown in figure. Although I should get variation in DC signal between 4 to 20mA. I cannot add or delete elements from the given circuit. Please help me to get a smooth DC signal at output which varies between 4 to 20mA with a particular range of variation in sensing element capacitance.

1583433351324.png
1583433411602.png
 

Thread Starter

irsarasheed

Joined Dec 24, 2019
31
Differential capacitor:
.View attachment 200753
Double check circuit and tune pots
Sir Sorry for bothering you again, but I have tried the method you suggested. I have also rechecked circuit connections.
1-Sir do you think the operational amplifiers are working properly. I think they are not getting required ±Vs, and the varying signal as a result of differential capacitance variation is not propagated to the output load resistance. (You have designed differential capacitor very well). Although LM108 datasheet says it has wide supply range from ±2V to ±18V(https://www.mouser.com/datasheet/2/609/lt0108-1268884.pdf ).
2-Probably Operational Amplifier 3 is not getting the input signal because i checked it also. The difference of I1-I2 (DC signal)is sent to this amplifier. I1 is the current through C3, I2 is the current through C2. But may be I am wrong.
3-May be there is problem for the ground connection at the load side. I am also attaching the potentiometer file this time. May be you can get better tuning option.
The target is to get DC signal (4 to 20mA) through load resistance by variation in differential capacitor.

Looking for your help again. Sir I understand that your time is precious. But I am unable to solve this problem. Waiting for your affectionate response.
 

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Danko

Joined Nov 22, 2017
1,005
1-Sir do you think the operational amplifiers are working properly. I think they are not getting required ±Vs, and the varying signal as a result of differential capacitance variation is not propagated to the output load resistance. (You have designed differential capacitor very well). Although LM108 datasheet says it has wide supply range from ±2V to ±18V(https://www.mouser.com/datasheet/2/609/lt0108-1268884.pdf ).
2-Probably Operational Amplifier 3 is not getting the input signal because i checked it also. The difference of I1-I2 (DC signal)is sent to this amplifier. I1 is the current through C3, I2 is the current through C2. But may be I am wrong.
Seems they are working:
1583543465503.png
And they need feedback by DC:
1583547743212.png
So, range of out voltage with feedback is from 0.75V to Vs-0.75V.
3-May be there is problem for the ground connection at the load side.
Emitter of Q4 should be grounded.
 
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Thread Starter

irsarasheed

Joined Dec 24, 2019
31
Okay sir, I am really Thankful to you. Sir the current through R19 should be a DC signal, Right? (Please correct me if I am wrong). Then why the current is in the form of pulses. Tuning potentiometers also do not help. Sir I find you expert in this field. Can you achieve this target by using given circuit diagram. 'Get DC signal (4 to 20mA) through load resistance by variation in differential capacitor'. I believe that your expertise will make it easier for you. I am reattaching the circuit files and really hope to get positive results.
1583576020653.png
 

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Thread Starter

irsarasheed

Joined Dec 24, 2019
31
Seems they are working:
View attachment 200847
And they need feedback by DC:
View attachment 200858
So, range of out voltage with feedback is from 0.75V to Vs-0.75V.

Emitter of Q4 should be grounded.
Okay sir, I am really Thankful to you. Sir the current through R19 should be a DC signal, Right? (Please correct me if I am wrong). Then why the current is in the form of pulses. Tuning potentiometers also do not help. Sir I find you expert in this field. Can you achieve this target by using given circuit diagram. 'Get DC signal (4 to 20mA) through load resistance by variation in differential capacitor'. I believe that your expertise will make it easier for you. I am reattaching the circuit files and really hope to get positive results.
1583580992559.png
 

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