I suggest you take a look at your HMI software, (what is it anyway?). It's possible you're already sitting on some type of protocol conversion software. I use Crimson 2.0 from www.redlion.net. It allows me to convert to .csv files that are easily adapted to Excel for any purpose you may need.
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"Do not worry about your difficulties in Mathematics. I can assure you mine are still greater". - Albert Einstein
The task you describe is what HMI software is all about - collecting, logging, saving data, some analysis tools, the classic 'historian'. Modbus is a communications protocol used to get the data (TCP is Modbus over ethernet).
Most Modbus master utility software tools (Modscan32, SimplyModbus) are very usable as test tools. For all I know they may be useable to collect and log data, but I haven't attempted done so.
RDGRNR alludes to the HMI aspect of your request in his advice to take a look at your HMI, but I suspect that you might not have HMI software.
There are literally hundreds of HMI packages. I've only dealt with licensed packages but Google finds lots of things represented as 'free' for whatever that means.
Basically i m already have HMI.I want to take data from HMI on PC .The HMI supports for modbus master/slave/TCP .same data i have collect on PC .i have one option SCADA but it is costly.Is there any tool to collect data on PC which is in .CSV format.