Internet PLC Forum
General => Technical support => Topic started by: can on February 25, 2014, 05:15:00 PM
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Hi. Currently, a load cell sends an analogue signal to an amplifier before hooking up to AB PLC. Is it possible to tap the analogue signal in order for FMD to monitor the signal as well?
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The signal from the load cell is typically small signal. In order to tap this signal and feed to an FMD PLC you will again need another amplifier (signal conditioner or instrumentation amp) to amplify this signal to the 0-5V range of the PLC's analog input. The high amplifier input impedance ensure that it does not affect the load cell output signal that goes to the amplifier for the AB PLC.
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Hi. What worries me is the integrity of the signal coming from the loadcell. Will there be any problem with supplying the same signal to 2 amplifier?
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Usually amplifiers have very high input impedance (> 10M ohms) so you can connect the same signal in parallel to multiple amplifier and it should not affect the signal integrity since the amplifier input draws very little current.
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Hi. Thanks for the clarification. If the analogue voltage is 10VDC, can the FMD88 take the extra voltage?
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You might want to use an external ADC such as the I-7017.
This ADC can be connected to the analog output of the load cell signal conditioner. The I-7017 can deal with 0..10 volt signals and it connects to the TriLog PLC via rs485.
The analog inputs to the I-7017 are differential the TriLog ADC inputs are single ended. Differential inputs help to overcome a lot problems with signal grounding between the 2 PLCs.
The input impedance of the I-7017 is grater than 20M ohm to both the signal and the ground (reference) inputs.
Best regards,
Gary d