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I actually have a PLC VIPA 200V which is exactly the same as a S7-300 CPU3152DP of Siemens (I even use Step7 to programm it). This question more than a Siemens question is a general question about analog input problem.
I have an universal analog input card (mV, RTD, TC, 4-20mA, 0-20 mA). All the inputs are passive inputs. I have connect a 4 wire brix transmitter (which is power supplied with 220 VAC) with an active analog output 4-20 mA to the channel 0. But I get the right value of the analog input for a few seconds (let's say I get a PEW280=4092 decimal)and then the reading goes to a 0 mA value (PEW280=-4096. I think this value is the one that shows). The reading is OK but the value is not stable. it's like the loop current wire get's a 0 mA signal.
I've checked the wiring and it's ok. there is no loose wire. To make sure, the transmitter is OK, I emulate a 4-20 mA signal loop with a Fluke 4-20mA emulator (I use a 24 VDC power with a Fluke 4-20 mA emulator and a external multimeter to measure the current in the loop I'm emulating) and the same not stable problem happened. When I did this emulation, I connect the wires directly to teh PLC to make sure there is no problems in the wiring. Then, In order to make sure the input card of the PLC is OK I disconnect the Brix transmitter and connect a 2 wire pH transmitter in the same analog input channel and the reading was ok and stable (there is no problem).
I really don't know what else to try. I've make all the possibles actions.
Please in case any of you had a similar problem before please let me know or at least give me your ideas or comments what else to try.
This is a new project and this brix reading value is very important for the process and I'm stuck on this problem.
Thanks in advanced for your help.
I have an universal analog input card (mV, RTD, TC, 4-20mA, 0-20 mA). All the inputs are passive inputs. I have connect a 4 wire brix transmitter (which is power supplied with 220 VAC) with an active analog output 4-20 mA to the channel 0. But I get the right value of the analog input for a few seconds (let's say I get a PEW280=4092 decimal)and then the reading goes to a 0 mA value (PEW280=-4096. I think this value is the one that shows). The reading is OK but the value is not stable. it's like the loop current wire get's a 0 mA signal.
I've checked the wiring and it's ok. there is no loose wire. To make sure, the transmitter is OK, I emulate a 4-20 mA signal loop with a Fluke 4-20mA emulator (I use a 24 VDC power with a Fluke 4-20 mA emulator and a external multimeter to measure the current in the loop I'm emulating) and the same not stable problem happened. When I did this emulation, I connect the wires directly to teh PLC to make sure there is no problems in the wiring. Then, In order to make sure the input card of the PLC is OK I disconnect the Brix transmitter and connect a 2 wire pH transmitter in the same analog input channel and the reading was ok and stable (there is no problem).
I really don't know what else to try. I've make all the possibles actions.
Please in case any of you had a similar problem before please let me know or at least give me your ideas or comments what else to try.
This is a new project and this brix reading value is very important for the process and I'm stuck on this problem.
Thanks in advanced for your help.