Connecting an amplified 3-wire transducer to STGM

I'm trying to use an amplified string potentiometer with an STGM input. The string pot is not a voltage divider, but provides a 0-10 V amplified output signal. It has 3 wires: positive excitation, signal, and ground. Both excitation and signal are referenced to the same ground. I don't see an appropriate connection diagram in Dewesoft X3 software or manual. I tried excitation to Exc+ (pin 1), signal to In+ (pin 2), and ground to both Exc- (pin 8) and In- (pin 7), but this doesn't seem to work. What's the recommended connection? By the way, I have other examples of 3-wire transducers in which the excitation and signal reference the same ground conductor.

Dear Joseph,

we would need some additional information about the sensor that is beiing used. Could you please provide a datasheet or a web link of the sensor?

Witch device are you using?

Best regards,

Rok

@Rok Kmetič

Here's a datasheet. This device is connected for 0-10 v output (not 4-20 mA).

Joe

Dear Joseph,

the STGM amplifier has excitation max 15V and 45mA. So we suspect that the reason for the sensor problems is insufficient power supply.

If it's possible please try to connect the sensor to an external power supply as marked in the picture below:

For better assistance please tell us which device are you using so we could have a better look into this issue.

Best regards,

Rok

@Rok Kmetič

I've found that the STGM can somewhat work with the SP3 string pot, using the setup shown (attached). The odd thing is that the full scale output advertised by the manufacturer is 10 V, but I only get 3.15 V at full scale. I don't know whether it's OK to connect the Exc- (8) and In- (7) inputs.

I measured the current draw on the Exc+ line, and found it to be 17 mA, so it doesn't exceed the STGM's specs. A photo of the current measurement setup is also attached. A Verivolt Encore 5C current shunt was put into the Exc+ line.

So, I would like you to answer:

1) Is there a problem connecting the Exc- (8) and In- (7) inputs? and

2) Why do I see 3.15 V full scale instead of 10 V?

Dear Joseph,

The 3-wire sensor has to be connected in single ended mode.

In DEWESoft this cannot be switched because the excitation has to be used and the amplifier goes into differential mode.

A short circuit between the pin7 with pin4 will be needed, this will manually connect the input as a 3-wire single ended mode with the power sensor.

Please note that the scaling of the sensor will then need to be corrected since the reference will not be GND but EXC-.

Best regards,

Rok

Hello Joseph and Rok,

Curious if you could elaborate on the outcome of this case as we are considering purchase of multiple of the same model string pots.

Thanks,

Glenn.

Glenn P. Siddens, PE

Senior Mechanical Engineer

Direct: 1.419.720.5878

Main: 1.419.866.6301

Email: [email protected]

@Glenn Siddens, we implemented the wiring diagram shown on the last post (posted 08.11.2019), and it works fine. The missing piece was connecting pins 4 & 7. We've come up with a universal cable design to connect the STG 9-pin to any transducer, and didn't want to change that cabling, so we use a short "pigtail" cable to attach the string pot to the universal cable. Since the 4-7 jumper is unique to the string pot, that connection is made in the string pot pigtail. The overall end to end wiring schematic (universal cable + pigtail) is shown below.

Hello Rok,

I will also be trying to connect a string potentiometer to Dewesoft and would like to understand if I will need to wire my D-SUB connector the same way you specified in your previous post. I will be using a string potentiometer from UniMeasure and the spec sheet is attached. I would be connecting this sensor to a SIRIUS, HD STG-S.

Thanks,

Kyle

Dear Kyle,

if you are connecting a potentiometer sensor to an STGS amplifier you can make a connection like mentioned above with selected ''Voltage measurement'', or choose a ''Potentiometer measurement'' from the drop-down menu. Both DSUB9 connections are made the same way. So you can choose which one gives better results.

Best regards.

Rok

Hi Rok,

I have finally received my string pot and have wired it per the information you provided and also included the jumper for pins 4 and 7. When I try to setup the sensor as a potentiometer and follow the values you listed, I get an OVL condition and do not get any data. If I setup the sensor as a voltage with the range set to 10V and the excitation set to 12V I start to get some data across a range from -8.9in to 6.0in. These values look to be accurate when compared to a tape measure, but not sure. How can I get this sensor to work as a potentiometer? What should my two points be if the manufacturer states the average sensitivity as 656.33333mV/inch? Would I need to have a power supply hooked up in order to use this sensor as a voltage?

Thanks,

Kyle

Dear Kyle,

the jumper is needed if an amplifier does not support potentiometer measurements. If you are using an HD-STGS you do not need the jumper between pins 4 and 7. That is the reason for the OVL message.

Would I need to have a power supply hooked up in order to use this sensor as a voltage?

There is no need for an external power supply. The sensor requires an Excitation Voltage 4.9 to 30 VDC and an Excitation Current 30 mA max:

HD-STGS can provide the power:

How can I get this sensor to work as a potentiometer? What should my two points be if the manufacturer states the average sensitivity as 656.33333mV/inch?

Connect the sensor 3 wires as described in the previous post. You can enter the values directly into the second point or a second option would be that you extend the string of the sensor to a known distance and read the voltage value. Then put both values as the second point.

Best regards.

Rok