D
We have an old probe which we would like to add some additional functionality by connecting it to a PLC for process control. The signal output from the probe is stated at being the following from the manual and I am looking for ideas as to what PLCs will accept this signal. Direct quote from the manual:
"The VisiWater DO sensor generates the 4 to 20 mA signals by pulse with modulation (PWM) which is not compatible to all PCS systems. Also a galvanic separation between the power supply and the PCS is necessary for correct sensor functionality when used in 4 to 20 mA setups."
There is also further detail about the signal:
"Hamilton VisiFerm DO sensors use the method of pulse-width modulation (PWM) to adjust the DC currents of the 4 to 20 mA interfaces corresponding to the measured values. In principle, the pulse width (ti) of a rectangular signal with a constant frequency, the pulse duty factor (ti/T), is modulated and afterwards demodulated by a low-pass filter to generate continuous analog DC signals. The resulting value yi corresponds to the average of the PWM signal (see Figures 12 and 13). The PWM-loads of the Sensors have low-pass filters which are not able to eliminate all AC fractions of the used PWM frequency of 5 kHz due to technical impossibilities. Therefore, the current signals of the 4 to 20 mA interfaces are still overlaid by a certain AC which should be masked by lag smearing or input filters of the current input card of the process control system (PCS). Recommended PCS settings are a sampling rate below 3.5 kHz, an averaging over more than 1 s, and the use of galvanically separated inputs to avoid oscillations. It is also possible to use mathematical functions or isolating amplifiers for signal processing filtering if necessary."
Any help and hardware recommendations will be gratefully accepted.
"The VisiWater DO sensor generates the 4 to 20 mA signals by pulse with modulation (PWM) which is not compatible to all PCS systems. Also a galvanic separation between the power supply and the PCS is necessary for correct sensor functionality when used in 4 to 20 mA setups."
There is also further detail about the signal:
"Hamilton VisiFerm DO sensors use the method of pulse-width modulation (PWM) to adjust the DC currents of the 4 to 20 mA interfaces corresponding to the measured values. In principle, the pulse width (ti) of a rectangular signal with a constant frequency, the pulse duty factor (ti/T), is modulated and afterwards demodulated by a low-pass filter to generate continuous analog DC signals. The resulting value yi corresponds to the average of the PWM signal (see Figures 12 and 13). The PWM-loads of the Sensors have low-pass filters which are not able to eliminate all AC fractions of the used PWM frequency of 5 kHz due to technical impossibilities. Therefore, the current signals of the 4 to 20 mA interfaces are still overlaid by a certain AC which should be masked by lag smearing or input filters of the current input card of the process control system (PCS). Recommended PCS settings are a sampling rate below 3.5 kHz, an averaging over more than 1 s, and the use of galvanically separated inputs to avoid oscillations. It is also possible to use mathematical functions or isolating amplifiers for signal processing filtering if necessary."
Any help and hardware recommendations will be gratefully accepted.