Seimens 0-10v analogue input.

We have a vacuum pressure sensor that has become faulty, unfortunately the original is obsolete but the manufacturer has supplied us with the replacement (these are manufactured by Festo). when the new sensor is fitted to the machine it is displaying a pressure of 145mBar on the HMI screen, this is when the machine is at rest and no vacuum is being generated. when the pressure sensor is disconnected from the analogue input 0v can be measured on the output, which correctly tracks the vacuum down to -1Bar, giving 10v output. if we measure the voltage on the analogue input card with the sensor disconnected we measure 2.3V.
we thought our new sensor may have been faulty but we have swapped it to a different machine and get the same results. this led us to think it may not be compatible, even though Festo assured us it is the correct unit, so we contacted the machine manufacturer. They have confirmed that we should only need to set the unit as 0-10V as the output type. This was already set correctly.
The old type sensor that was removed from our second machine was connected to the first machine and the readings are all correct on the HMI.
Can anyone suggest a way to resolve our issue or give us some checks to carry out?

I have attached an image of the input connection details for the machine.
The input card is a Siemens 6ES7134-4FB52-0AB0 which is located in an ET200 remote rack.

Is the scale on the old unit the same as the one on the new unit ??

Yes both units are 0-10V with a 0 to -1Bar range.

give us the old and new sensor typenumbers, probably the festo is setup as 2-10Volt. or even 4-20mA.
checck also if the 0Volt is proper connected.

Original part FESTO SDE1-V1-G2-HQ4-C-P2-M8
new part FESTO SPAU-V1R-H-G18FD-L-PNLK-PNV

There doesn't appear to be any way to configure the output on the original unit, but the new one has 3 options and we have selected 0-10V.

I have not checked the original sensor output when it is not connected to the plc.

CRMCC said:

if we measure the voltage on the analogue input card with the sensor disconnected we measure 2.3V.

Click to expand...

Between which points are you measuring to get significant voltage on an open input?

Had a similar problem on a press with obsolete parts. Get a 0 to 10V signal conditioner. Install adjust to suit and you are good to go.

danw said:

Between which points are you measuring to get significant voltage on an open input?

Click to expand...

We split the input at position A.
At the instrument we have 1.45V (position a).
At the PLC we had 2.3V (position aa).

And the Siemens card is configured for voltage? Even though it worked before...

CRMCC said:

We split the input at position A.
At the instrument we have 1.45V (position a).
At the PLC we had 2.3V (position aa).

Click to expand...

If you opened the circuit at A, then 1.45V at point a is the transmitter's output. An output of 1.45V corresponds to the -145mbar reported value by the Siemens AI.

So the Siemens is reporting the same value as the transmitter is producing.

Either the pressure system has a slight vacuum on it which the Festo is correctly reporting, or the Festo is faulty, incorrectly reporting a slight vacuum pressure when there is no vacuum, or the 1.45V is an offset due to a ground loop, possibly between one AI channel.

Which pins are you wiring to on the sensor?

danw said:

If you opened the circuit at A, then 1.45V at point a is the transmitter's output. An output of 1.45V corresponds to the -145mbar reported value by the Siemens AI.

So the Siemens is reporting the same value as the transmitter is producing.

Either the pressure system has a slight vacuum on it which the Festo is correctly reporting, or the Festo is faulty, incorrectly reporting a slight vacuum pressure when there is no vacuum, or the 1.45V is an offset due to a ground loop, possibly between one AI channel.

Click to expand...

You are correct, the 1.45V is when it is connected to the input, it measures 0V when disconnected. We also have a second new Festo unit as it is now a stock item and this produces the same results.

spaderkung said:

And the Siemens card is configured for voltage? Even though it worked before...

Click to expand...

The machine manufacturer says it is, but I am unable to confirm this.

AustralIan said:

Which pins are you wiring to on the sensor?

Click to expand...

pin 1=24V
pin 2= input to PLC
pin 3= 0V
pin 4= unused (it is a digital out)

Was the sensor wired to m+ before on the PLC card? Had it been a 24v active sensor for mA then the plc input should be m- I think. The same might apply to voltage input cards. M+ cold be card sourcing.

Just a little confused, a SDE1-V1-G2-HQ4-C-P2-M8 is a two PnP digital output unit not analogue.

nehpets said:

Just a little confused, a SDE1-V1-G2-HQ4-C-P2-M8 is a two PnP digital output unit not analogue.

Click to expand...

Yes that does seem to be the case when checking the part number, but it does have the analogue output 0-10V, which should make it a SDE1-V1-G2-HQ4-C-PU-M8.
The whole thing just gets more confusing, thought that speaking with the OEM would have cleared things up, but we are still none the wiser. It's lucky we have an option to turn the vacuum check function off.