Analog input nightmare - Showing my lack of experience

Hi All,


I have wired up plenty of sensors and plenty of digital things over my time. However my exposure to analog cards and sensors is very limited, but I have done it.


However it isnt working. I confidently told the customer to order the parts and thought I could sort it, but I just cant get a value out of the device...


Maybe I am just being thick.


I have an LKM445 sensor and connecting to a 6ES7134-6HB00-0CA1 on a 1516 PLC.


Set it up as a 2 wire 4-20ma transducer as per the attached screenshot. Wired up the +24VDC terminal on the sensor terminal 5 of the input card and the T+ terminal to terminal 9 of the input card. I get absolutely nothing, I get wire breaks, no scaling or anything works out.


Any ideas that I can try? I have tried an external 24vdc+ supply to the sensor. Changing every setting around 4-20ma 2 wire in TIA... I think I just dont understand the principles.

A common mistake is to set up the sensor as a 2-wire in the software, when in fact it is a 4-wire sensor. In your case, it is a 4-wire (or 3-wire) sensor.

2-wire means the sensor is powered by the analog module.
4-wire (or 3-wire) means the sensor is powered by 24VDC externally.

Your JPGs dont display.
Be sure that size in height, width and kB do not exceed the alowable.

Anyway, the sensor is a little weird as it has one 24V power supply input and two analog outputs. There is no common ground. So it is not really two 2-wire sensors, or two 4/3-wire sensors.
Since the power supply to two signals are mixed together, I would not try to supply the 24V from the PLC AI card. The PLC AI card is designed for independent channels. Instead supply the 24V from an external source.

So I guess you should set it up as 4-wire in TIA, and then connect it like this:
Sensor terminal :+ = 24V from your power supply.
Sensor terminal :T = AI module terminal 5.
Sensor terminal :H = AI module terminal 6.
Common 0V from your power supply to AI module terminals 7 and 8.

sigmadelta said:

A common mistake is to set up the sensor as a 2-wire in the software, when in fact it is a 4-wire sensor. In your case, it is a 4-wire (or 3-wire) sensor.

2-wire means the sensor is powered by the analog module.
4-wire (or 3-wire) means the sensor is powered by 24VDC externally.

Click to expand...

JesperMP said:

Your JPGs dont display.
Be sure that size in height, width and kB do not exceed the alowable.

Anyway, the sensor is a little weird as it has one 24V power supply input and two analog outputs. There is no common ground. So it is not really two 2-wire sensors, or two 4/3-wire sensors.
Since the power supply to two signals are mixed together, I would not try to supply the 24V from the PLC AI card. The PLC AI card is designed for independent channels. Instead supply the 24V from an external source.

So I guess you should set it up as 4-wire in TIA, and then connect it like this:
Sensor terminal :+ = 24V from your power supply.
Sensor terminal :T = AI module terminal 5.
Sensor terminal :H = AI module terminal 6.
Common 0V from your power supply to AI module terminals 7 and 8.

Click to expand...

Brilliant stuff. I like this. I had no idea. I will do this and report back

A tip on how to figure out how to connect non-standard current transmitters:
Look at the circuit diagram for the AI module.
Follow the signal path for current inputs.
You will see on each channel that there is a shunt resistor.The shunt resistor converts the current signal to a voltage that the ADC in the AI module can read.
So you have to make a path for the current signal to pass through the shunt reistor.
When you connect an externally powered signal to the input terminal, you have to send the current back to the power supply via the other side of the shunt resistor.

Oh, one last thing.

An advantage of using the power supply from the AI module, is that you then will have current limiting built-in. That protects the AI module, for example against someone messing up and putting 24V directly on the analog input. That would damage the shunt resistor.
So if you go by my advise and supply the 24V from an outside source, you then have the risk of damaging the card. Because of that it may be prudent to install a fuse in each channel, to protect the AI card. It depends on how probable you estimate it to happen, and how bad you estimate the consequences to be. It is not a big deal if a channel gets burned, you just replace the AI card.

JesperMP said:

Your JPGs dont display.
Be sure that size in height, width and kB do not exceed the alowable.

Anyway, the sensor is a little weird as it has one 24V power supply input and two analog outputs. There is no common ground. So it is not really two 2-wire sensors, or two 4/3-wire sensors.
Since the power supply to two signals are mixed together, I would not try to supply the 24V from the PLC AI card. The PLC AI card is designed for independent channels. Instead supply the 24V from an external source.

So I guess you should set it up as 4-wire in TIA, and then connect it like this:
Sensor terminal :+ = 24V from your power supply.
Sensor terminal :T = AI module terminal 5.
Sensor terminal :H = AI module terminal 6.
Common 0V from your power supply to AI module terminals 7 and 8.

Click to expand...

Well blow me down with a feather. That works!


However the numbers are really weird, but it is clearly wired correctly. The scaling in the manual is supppper complicated. One bit of a word tells you there is no fault then it seems it depends what mode to have another bit tell you something else. I thought in TIA it was supposed to be easier??


I might as well ask. Any advice on how on earth to work out which bit is actually the temperature?

BMW
Come on, all these years working on Siemens plcs you haven’t scaled analog?
From your sensor 4-20ma will be x to x temperature
That’s 0-27648 raw value
Just use the various scale instructions in Portal

Easier than working on a BMW car

a scale block

A Scale Block
I like this one, but Im old school

JRW said:

A Scale Block
I like this one, but Im old school

Click to expand...

Amazingly I actually dont think I ever have! I have done a lot of things but analog seems to not be one.


I did it already. But thanks

JRW said:

Easier than working on a BMW car

Click to expand...

Or using the indicators!