Dear Sir or Madam,

My customer is now using PV750 and is considering to use pressure sensor (0-5V output) with PV750 by configuring analog input in PV750. In case of using 0-5V sensor with PV750, I think they should valid an analog input and set it up to 0-5V via PowerVision. Is there any program they should make other than this? If yes, please kindly let me know what program they should make and how they should do that (it helps them if there is any sample config data).

The specification of pressure sensor they are using is as below.

Pressure range: 0 to 25MPa
Voltage range: 1 to 5V
(This sensor output varies in a linear manner.)

Your kind support would be much appreciated.

Best regards,

Toshiki Takehara

Hi,

Attached is a PV750 I/O configuration. This configuration uses all the Analogs and Digitals. This might give you some idea.

Hope it helps.

Puplaonkar
FW Murphy

Dear Puplaonkar,

Thank you for your prompt reply and the sample configuration.

Although this config data shows raw analog input data, our customer would like to calculate the raw data (1 to 5V) to pressure value (0 to 25MPa) and show it on main page. When they used an ES2F fuel sender with PV750, they made a script to calculate the raw data (resistance value) broadcasted from fuel sender to percentage (0 to 100%). So, I think that they need to make a script for pressure sensor like the case of fuel sender. Do you have any sample script to calculate the raw data as they want? Or, please kindly advise me how they should make a script.

Best regards,

Toshiki Takehara

Dear Puplaonkar,

I tried to make a configuration referring to your sample data, but I did not.

Our customer wants to conver the raw voltage output sent from pressure sensor to the pressure value and show it to the display on PV750. In this case, they should make a script to convert the voltage output to pressure value, is my understanding correct? If yes, could you please let me know how they should make such a script? We would also much appreciate if you make a sample config data and send to me becasue I am not familiar with programming.

Their sensor specifications are as below.

Sensor Manufacturer: WIKA
Part Number: PSD-31
Voltage Output: 0 to 5VDC
Pressure Value: 0 to 25MPa

Conversion point,
Voltage Output 1V 2V 3V 4V 5V
Pressure Value 0.00MPa 6.25MPa 12.50MPa 18.75MPa 25.00MPa

* Output characteristic is varied in a linear manner.
** The output of this sensor is originally 4-20mA current output but they convert it to 0-5V voltage output by converter.

If you need further information, please kindly let me know.
Thank you very much for your kind support and help to this matter.

Best regards,

Toshiki Takehara

The PV750 analog input is actually 0 to 4 Volts using a 10 bit Analog to Digital Convertor (ADC). What you see in the "30 PV750 IO.murphyConfig" is the ADC count which can be converted into a voltage. (The following is the actual voltage to count measurements for a PV750; [Voltage, Count], [0.0V, 0 Count], [0.204V, 51 Count], [1.000V, 256 Count], [2.000V, 512 Count], [3.000V, 769 Count], [4.001V, 1023 Count], [5.001V, 1023 Count] ).

There is a problem with your sensor conversion from 4-20 mAmpere sensor to a 0 to 5 Volt sensor. The PV7500 analog input is limited to 0.0 to 4.0 Volts. Therefore you cannot use 0.0 to 1.0 voltage range (because it is negative pressure) and you cannot use the 4.0 to 5.0 voltage range (because you will only get the 1023 maximum count).

I'm guessing that you converted from a 4-20 mAmpere sensor to a voltage sensor by putting a 250 Ohm resistance in parallel with the 4-20 mAmpere device. This gives you the 1 V to 5 V range. If you switch the 250 Ohm resistor for 200 Ohms you will move the Analog Voltage range down to 0.8V (for 4 mAmperes) and 4.0V (for 20 mAmperes). The Pressure curve remains linear with the following values: [0.8V, 0 MPa], [1.6V, 6.25 MPa], [2.4V, 12.5 MPa], [3.2V, 18.75 MPa] and [4.0V, 25 MPa]. Using the slope intercept linear equation (y=mx +a) you get Y MPa = (7.8125 * (X Volts)) - 6.25.

Each count is 0.00391 volts. So the above equation becomes Y MPa = (0.03057 * count) - 6.25 to see the pressure in MPa.

You need to create a fuel pressure variable which measures a voltage that converts a count from IO.Input Channel 1 into pressure with the above equation. (See the [Database] Tab select the [Input Output Port Manager] Programming Item and the FuelPressure variable.)
You also wanted to create a percent fuel gauge based on the count values from IO Input Channel 1. The count at 0 percent is 204 with an input voltage of 0.8 volts. The count at 100 percent is 1023 with an input voltage of 4.0 volts. To calculate the percent you need to subtract 204 from the count and scale the value from 0 to 1 by dividing by (1023-204). (See the [Database] Tab select the [Input Output Port Manager] Programming Item and the PercentFuel variable and how the value is calculated.)
Add two text gauges (or bar gauges or Curved Bar Gauges) for these variable to the display page. Specify the smallest increment to be the number of decimal digits. Specify the range from 0 to 30 MPA or 0 to 100% to avoid negative values.
Last but not least you need to add a State Machine to recalculate the Fuel Pressure and Percent Fuel values. A state machine represents a thread of control for a task which is to update these fuel values once a second. The initial state is where the task lands after power on. Upon entering this initial state we call the transition timer (OneShotStartUp) to wait 5 seconds before transitioning to the UpdateFuel State. The UpdateFuel State triggers recalculations of the Fuel Presssure and Percent Fuel using the reoccuring GetNewFuelCountTimer. The GetNewFuelCountTimer is provided in the transition which loops upon the UpdateFuel State.
I've enclosed another configuration. Let me know if you have any questions.
Thanks,
Phil Cebuhar

Dear Phil,

Thank you very much for the sample configuration data and kind explanation.

If they use the sensor with existing 0-5 input voltage, the pressure value can be shown only between 0.0 to 18.75MPa because PV750's analog input is limited to 0.0 to 4.0V (pressure value at 4.0 to 5.0V, 18.75 to 25.00MPa cannot be shown). Is my understanding correct?

Do you have an idea to make a script to convert the input 0-5 voltage to 1-4 voltage, and then convert 1-4 voltage to pressure value (for example, Y Volts = {(Input Voltage) * 0.6} + 1.0)? If such double conversion is not possible, we will suggest them to reduce the input voltage according to your instruction.

Best regards,

Toshiki Takehara

Dear Takehara-san,
You are correct that if you uses the existing sensor set up for 1.0 to 5.0 Volts that you would only be able to see 0 to 18.75 MPa values.

While a double conversion is certainly possible in the software, you cannot get around the problem that your hardware is not measuring 18.75 to 25.0 MPa from the sensor.

A hardware fix would be difficult (in my estimation). You would need to offset the sensor voltage with an Op-Amp so that the range would be from 0.0 to 4.0 Volts instead of 1.0 to 5.0 volts. It is a lot of extra equipment to make the wrong display work correctly.

You can use a different display which will measure from 0 to 5.0 Volts or also directly supports 4 to 20 mAmpere sensors. The PV780 (same size LCD display as the PV750) has 3 analog input which each supports 0 to 5.0 Volts and/or 4 to 20 mAmpere sensors based on the configuration. The PV450 (a smaller display) has one analog channel which can be configured to 0 to 5.0 Volts and/or 4 to 20 mAmperes, again based on the configuration. The PV780 and PV450 displays are being supported in the PowerVision 2.6.2xxxxx latest version while the PV750 is not. The PV780 has more features than the PV750 which is why the PV750 is less favored.
Thanks,
Phil Cebuhar

Dear Cebuhar,

Thank you very much for your reply.

I understand that it is better for our customer to decrease the voltage output to 0.0 - 4.0V (or use 4-20mA). I will advise your suggestion to them and also offer to use the PV780 in the future if they still want to use 1.0 - 5.0V output.

Best regards,

Toshiki Takehara