Fasthotrod
Member
Good afternoon everybody!
I was recently tasked with a project and I think that my solution will be to integrate a PLC into it, but I'm not very familiar with PLC programming so I don't know if it's possible to do it easily or if I'll be getting in over my head.
Here is the situation: We are replacing a standby power system at a facility. The facility has a "legacy" computer system (legacy meaning: old) that monitors the entire facility, including the power system. The legacy system provides a readout on both a local and a remote computer terminal.
The new power system that is being installed is not compatible with the legacy system, and the legacy system cannot be modified.
Therefore, I need to come up with a solution that can get the information from the new power system and sends the proper signals to the legacy system.
I am looking at the following parameters for the power system:
AC Voltage: 0-150 VAC (x3 phases)
AC Current: 0-150 Amperes (x3 phases)
AC Frequency: 60 HZ
Transfer Switch Position: Commercial or E/G
Generator Battery Charger Current: 0-10 Amperes DC
Generator Oil Pressure: 0-75 PSI
Generator Water Temperature: 0-220 Degrees C
Generator Oil Pressure Alarm
Generator Temperature Alarm
Generator Over-Speed Alarm
Generator Over-Crank Alarm (Starter Time Out)
The Legacy system expects to see the following input:
AC Voltage: 0-5 VDC (x3 phases)
AC Current: 0-5 VDC (x3 phases)
AC Frequency: 120 VAC @ 60 HZ
Transfer Switch Position: NC Contacts
Generator Battery Charger Current: 0-5 VDC
Generator Oil Pressure: 0-100mV DC
Generator Water Temperature: Unknown at this time...
Generator Oil Pressure Alarm: NC Contacts
Generator Temperature Alarm: NC Contacts
Generator Over-Speed Alarm: NC Contacts
Generator Over-Crank Alarm (Starter Time Out): NC Contacts
I realize that I can just install voltage, current, temperature and pressure transducers with a 0-5 VDC output to feed the legacy system, but there are a couple of inputs that are a bit more complicated. (One input is 0-100 mV input for example.)
So it got me thinking... what if I were to use a PLC that acts as an "interrupter?" I could take the various inputs from the power system and use the PLC to scale them to whatever output I need.
For example, the legacy system expects to see a 0-5 VDC signal for an input voltage of 0-150 VAC. I could use a voltage transducer with a 0-5 VDC output, or I could use a transducer with a 4-20mA output, and use the PLC to give me an output of 0-5 VDC. I would think that there is a simple way to do this, correct?
The same holds true for the oil pressure reading. I could use an oil pressure transducer with a 4-20 mA output and use the PLC to convert it to 0-100 mV output. (The legacy system has a high impedance input, so I'm thinking I could use a 0-20 mA output from the PLC and use a simple resistor network to get the voltage I am looking for.)
The coolant temperature reading is a bit more complicated. The legacy system supplies -15 and +15 VDC to a solid state temperature sensor which provides a linear output based on the temperature. The sensor reads 1000 ohms at 25 C. The temperature sensor provides a voltage/current input to a variable gain amplifier, which then converts the signal to 0-5 VDC from 0-220 C. I'm currently working on the existing circuits to see if I can come up with something that will work with the PLC output... I'll add more to this part as I learn more about the circuit.
One more thing: The replacement power system has the ability to communicate via RS-232 and RS-434 using MODBUS. I believe that I can use the PLC to get the information I need from the power system, then have the PLC give me the respective output.
So what do you all think... am I off my rocker, or is this something that can be done (relatively) easily?
Thanks in advance.
Mark
I was recently tasked with a project and I think that my solution will be to integrate a PLC into it, but I'm not very familiar with PLC programming so I don't know if it's possible to do it easily or if I'll be getting in over my head.
Here is the situation: We are replacing a standby power system at a facility. The facility has a "legacy" computer system (legacy meaning: old) that monitors the entire facility, including the power system. The legacy system provides a readout on both a local and a remote computer terminal.
The new power system that is being installed is not compatible with the legacy system, and the legacy system cannot be modified.
Therefore, I need to come up with a solution that can get the information from the new power system and sends the proper signals to the legacy system.
I am looking at the following parameters for the power system:
AC Voltage: 0-150 VAC (x3 phases)
AC Current: 0-150 Amperes (x3 phases)
AC Frequency: 60 HZ
Transfer Switch Position: Commercial or E/G
Generator Battery Charger Current: 0-10 Amperes DC
Generator Oil Pressure: 0-75 PSI
Generator Water Temperature: 0-220 Degrees C
Generator Oil Pressure Alarm
Generator Temperature Alarm
Generator Over-Speed Alarm
Generator Over-Crank Alarm (Starter Time Out)
The Legacy system expects to see the following input:
AC Voltage: 0-5 VDC (x3 phases)
AC Current: 0-5 VDC (x3 phases)
AC Frequency: 120 VAC @ 60 HZ
Transfer Switch Position: NC Contacts
Generator Battery Charger Current: 0-5 VDC
Generator Oil Pressure: 0-100mV DC
Generator Water Temperature: Unknown at this time...
Generator Oil Pressure Alarm: NC Contacts
Generator Temperature Alarm: NC Contacts
Generator Over-Speed Alarm: NC Contacts
Generator Over-Crank Alarm (Starter Time Out): NC Contacts
I realize that I can just install voltage, current, temperature and pressure transducers with a 0-5 VDC output to feed the legacy system, but there are a couple of inputs that are a bit more complicated. (One input is 0-100 mV input for example.)
So it got me thinking... what if I were to use a PLC that acts as an "interrupter?" I could take the various inputs from the power system and use the PLC to scale them to whatever output I need.
For example, the legacy system expects to see a 0-5 VDC signal for an input voltage of 0-150 VAC. I could use a voltage transducer with a 0-5 VDC output, or I could use a transducer with a 4-20mA output, and use the PLC to give me an output of 0-5 VDC. I would think that there is a simple way to do this, correct?
The same holds true for the oil pressure reading. I could use an oil pressure transducer with a 4-20 mA output and use the PLC to convert it to 0-100 mV output. (The legacy system has a high impedance input, so I'm thinking I could use a 0-20 mA output from the PLC and use a simple resistor network to get the voltage I am looking for.)
The coolant temperature reading is a bit more complicated. The legacy system supplies -15 and +15 VDC to a solid state temperature sensor which provides a linear output based on the temperature. The sensor reads 1000 ohms at 25 C. The temperature sensor provides a voltage/current input to a variable gain amplifier, which then converts the signal to 0-5 VDC from 0-220 C. I'm currently working on the existing circuits to see if I can come up with something that will work with the PLC output... I'll add more to this part as I learn more about the circuit.
One more thing: The replacement power system has the ability to communicate via RS-232 and RS-434 using MODBUS. I believe that I can use the PLC to get the information I need from the power system, then have the PLC give me the respective output.
So what do you all think... am I off my rocker, or is this something that can be done (relatively) easily?
Thanks in advance.
Mark