How should the host computer be configured to match the actual operating current of the frequency converter?
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Generally, larger motors require current monitoring. In the case of motors controlled by frequency conversion, the inverter outputs an analog signal to the analog input terminals of the PLC or DCS. How should it be configured so that the value displayed on the upper-level computer matches the current flowing in the motor?
The analog output of the frequency converter can be divided into two types: frequency feedback and the converter current, with 4-20mA signals provided to the DCS. But generally speaking, it’s used less often!
Basically, for larger motors, it is necessary to monitor the motor current, that is, the operating current of the inverter. This is quite useful; basically, motors with a power of over 30KW require current feedback.
I think the issue mainly lies in the parameter settings of the frequency converter; it is sufficient for the current output by the frequency converter to match the 4-20MA analog signal. Since, during DCS configuration, one only needs to know the current range corresponding to 4-20MA, the correct current value can be displayed on the configuration screen.
MM440 terminals 12, 13 (analog output 1) are connected to the PLC analog input module (4-wire 4~20mA): P771=27, P777=0, P778=4, P779=50, P780=20; 0A corresponds to 4mA； 50A corresponds to 20mA. I’ve never done this before; I always obtain the actual frequency and current values through communication. If it’s an analog output, setting it up using an MM4 inverter should work, I guess, hehe.
This post was last edited by zhaohh3211 on 2010-10-18 07:48. When configuring the upper-level and lower-level units, do you set the rated current of the frequency converter to a certain value, or what?
This post was last edited by zhaohh3211 on 2010-10-18 07:50. For Schneider frequency converters, the configuration requires a value that is twice the rated current of the converter; I’m not sure how it’s configured for other brands
Why choose a current that is 2 times the rated value? Isn’t it the case that 4mA corresponds to 0A and 20mA corresponds to the rated current?
This post was last edited by zhaohh3211 on 2010-10-18 07:50. A rated current of 20mA doesn’t seem quite right; there are sometimes sudden high currents that pose a safety risk. I think this value could be set higher, right?
This post was last edited by lzs771010 on 2010-10-17 at 18:50. The issue raised by the moderator is determined by the internal current sensing elements of the inverter. Just as you use a transformer and ammeter to monitor the current of a motor that starts directly, how do you configure this on the upper-level system? Regardless of the motor’s rated current, it is necessary to consider the range of the transformer. For example, if the motor is 15KW with a rated current of 30A, and you choose a transformer with a ratio of 80/5, then when configuring the upper-level system, you set 80 and 20MA to correspond to 80A. Inverters are different; no one knows the range of their sensors, and one can only find this information in the user manual. As to how the parameters correspond to each other, the sensor range may vary depending on the manufacturer. I hope everyone can share their personal opinions.
This post was last edited by zhaohh3211 on 2010-10-18 07:53. How to configure it on the host computer? I don’t seem to have understood what the person above meant. Just make a conversion in the program or in the screen configuration; it’s the Siemens FC105.