Internet PLC Forum

At the moment you can use a MOXA LAN to RS232 converter model DE311. You can then establish a TCP/IP connection to the PLC. Other RS232 to LAN converter can also be used.

TRi plans to introduce a Ethernet to RS232 converter in 1st quarter 2004 that will incorporate a subset of the TLServer functionality so that one or multiple M-series PLC may be accessed on the LAN  without the need for a PC to host the TLServer.  Look out for the announcement 1Q next year.

Let try to see If I understand you correctly:

1)  you are trying to measure the frequency of the output signal from the VFD which gives you a measurement of the current?

2) This VFD output is to be connected to input #3 of the PLC?

3) YOu are currently using the PMON function to measure the frequency using PULSEFREQUENCY function, but the reading obtained is unstable?

4) You are trying to convert the variable frequency output signal from the VFD into an analog value and feed it to the ADC #n of the PLC?

Let me know if any of the above assumption is not true. I am really not sure what impedance value are you looking for. If it is the input #3 then I am not sure whether we can say exactly what is the "input impedance" since the inputs are NPN type. The resistance in the path of the NPN inputs is 10K ohm.

If you are refering to the analog input (0-5V) then the input impedance is 1 M Ohm or higher.

I am not sure what is your objective. Are you using the PLC's PWM output to control the VFD? Normally VFD are either controlled by a analog input or a RS232/RS485 input. If your VFD can be controlled by RS485 that is the best way as you can get perfect values into the VFD. Although the PWM output may be low pass filtered to produce a pseudo analog output it may still be too noisy for device. We don't have a ready formula for such computation. You can try out the RC value they suggested to see if it will work better.

What is the coil voltage? Is it a DC 24V or AC voltage? If it is DC 24V coil and driven by the solid state output from the PLC then no need to add diode as there is built-in flyback diode. But if you use relay output of the PLC then you should add a diode to absorb the inductive kick.

However, if your coil is 120VAC and you are using the PLC's relay output (that's the only choice) then you can use a varistor to absorb the inductive spike. But if the current to drive the coil is low then use of varistor is not necessary.

You can use the TRiLOGI "Set PLC Real Time Clock" function under the "Controller" pull down menu to set the real time clock.

Once the real time clock is set to the value you defined, then you can use Online monitoring and click the "View Variable" to look at the new value of the RTC. It must work.

When you said "nothing happen" I think you are probably refering to what you display on the LCD? If your program does not refresh the LCD display regularly then the display will not show the new value even after you have set the new RTC data.

The easiest type of sensor to use it one that output 0-5V which can be connected directly to the PLC's analog input. Of course you need to ensure that if the sensor has its own power supply then the sensor's ground must be common with that of the PLC's 0V.

If your sensor output 4-20mA, you can convert the current into 1 to 5V voltage using a 250 Ohm resistor (read your installation guide for the wiring method). Both 2-wire and 4 wires types can be used.

Will, I am a little confused. You mentioned that you tried the reset instruction described in this post to no avail. Yet you mentioned that when you went to the site later you found that the PLC is running properly. Does it mean that initially you tried the instruction remotely? How were you able to turn ON DIP Switch and perform the reset if you were not at the site?

If your PLC gets back to running properly after a overnight shutdown without your manual intervention or transfering the program to the PLC, then it is likely that it RAM copies of the PLC CPU has been corrupted by the electrical noise in the system but the EEPROM copy is still intact. So after a power down and reset, the PLC runs the program properly again.

Protecting the supply to the PLC is important. Power to the microprocessor electronics is like life blood to human being. The PLC I/O circuit already filtered most of the noise coming from the  I/O but the power supply noise goes directly to CPU.  

Diesel/gas power generator are pretty noisy fellow. However, most power surge filter on the market are for AC circuit. You may want to try to search for a DC power filter to improve the reliability of your system.

Can you try to transfer one of those simple sample program to the PLC and then power OFF and then ON the PLC again. Check if the PLC goes into PAUSE mode again. We want to be certain if it is due to your application program or there is some hardware problem in the EEPROM.

If the PLC pauses after reboot even with the simple demo program, then most likely the EEPROM chip may have suffered some damage during the power outage. You should email us at support@tri-plc.com providing us your full contact address and we can make arrangement for replacement of the PLC or the EEPROM chip.