I am using the pseudo axis funtion of the molding firmware to measure accumulator position in blowmolding applications. I have commissioned 8 machines with retorfits from Maco 8000 to Siemens S7-300 solution using the RMC100 for position based parison control. At this time, I have encountered a problem on a machine where I am getting a position indication of -32768 when my scaled zero input voltage drops below the value saved in zero scaling register. On all other machines I get a valid value, -.100, for example. I have checked my input and am not seeing my transducer input disconnect from the Delta, which is what the value of -32768 in the display would indicate. Any ideas of what I should be looking for as the source of my problem?
When the counts read -32768 this indicates that the input voltage is below 0 counts (in position mode 0 volts = 100 counts). As you mentioned, this usually indicates that you have a broken wire. This is caused because internally the analog input are pulled to the -15V DC rail.
I would first check the “Input Cmn” pin on the analog cards 8 pin connector (pin 7). This MUST be connected to the common signal from your input signal. The other transducers may have the same source as the RMC itself but the common on each card is isolated from all the other cards. If you are using a PLC to generate your reference signal to Input #1 then I would make sure that its Input Cmn is connected to the PLCs output. The PLCs analog output probably has an isolated power supply too, and that is where our common needs to connect to.
Hope this helps.
Sr Application Specialist.