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Power-User

Join Date: Aug 2007
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Selection of an Encoder Signal Amplifier

09/01/2021 6:42 AM

Hi;

I need an equipment to amplify 12vdc encoder pulses into 24vdc. Do you please let me know any reliable equipment for this purpose? The Fatek PLC (FBs-40MCR2-AC) which i want to use here, accepts only 24VDC (+/-10%) signal. Both, PLC and encoders, are in stock but problem is that the encoders are 12vdc but PLC is 24vdc.

No-of-encoders = 06

Channels = A & B

Max Freq = 2KHz

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Guru

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#1

Re: Selection of an Encoder signal amplifier

09/01/2021 8:40 AM
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Guru

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#2

Re: Selection of an Encoder Signal Amplifier

09/01/2021 1:37 PM

Adjustable Voltage Regulator, DROK DC to DC 5.3V-32V to 1.2V-32V 12V Power Supply Module, 12A LCD Step Down Volt Transformer 160W CC CV Buck Converter Reducer

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Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

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#3

Re: Selection of an Encoder Signal Amplifier

09/01/2021 2:00 PM

Did you look here?

I did a quick look for this PLC to see if that company has an encoder interface module. I may have bad news. It doesn't look like this PLC has motion control capabilities to merit an incremental encoder interface.

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Guru

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#4

Re: Selection of an Encoder Signal Amplifier

09/01/2021 11:15 PM

While you have 6 inputs that are plenty high speed, you will be usually working with double ended power supplies, which might give you possible negative excursions if you sample only half of the pulse train. A PLC with encoder inputs is probably a better bet as Redfred notes.

Noise immunity for single ended encoders is pretty poor, if you don’t have the nicest environment.

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Guru

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#7
In reply to #4

Re: Selection of an Encoder Signal Amplifier

09/01/2021 11:43 PM

If you want both channels A and B, you really need 12 inputs, it may not be reliable to mix A & B inputs on different speed input channels. The software to test the input state of these 12 channels could be tricky. The speed of the inputs may or may not be suitable for pulse trains on every group, the software may need to be written with hardware interrupt calls for each input, which the designer may not have taken into account when the PLC was designed. I can see a flood of calls with stack overflow if you have the PLC doing anything else, like servicing a serial output USART chip.

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Guru

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#5

Re: Selection of an Encoder Signal Amplifier

09/01/2021 11:26 PM

I guess your signals are less than 10Khz?

Use a simple NPN transistor array - such as SMA4036. If the inputs are pulled to ground then it is straight forward, if it needs to be "pulled up" add a pull up transistor.

You will need a series resistor in the base of the transistor.

Breadbaord it and see what happens.

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Power-User

Join Date: Jan 2009
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#6

Re: Selection of an Encoder Signal Amplifier

09/01/2021 11:36 PM

I would use a small prototyping PCB to hold a quad comparator chip (e. g., LM 239P, the industrial version of the LM339P) and a dual comparator chip with similar characteristics (e. g., LM 293P). Run the power supply pins on 24 V (up to 400 mA at 24 V is available from the PLC to drive external accessories such as this). Add a voltage divider set to get 6 Volts (6.2 K and 18 K should work) to drive the inverting inputs of the comparators and connect your six encoder outputs to the non-inverting inputs. 24 K (1/8 Watt) pull-up resistors from the comparator outputs to +24V should provide adequate drive for the PLC inputs (the parts mentioned have open-collector outputs; push-pull outputs are typically limited to 16 V). Don't forget the power supply bypass capacitors, and leave space on the board to put in hysteresis resistors if needed. The hard part is packaging the board and connector selection - that depends on the operating environment.

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