Tachometer Conversion

[stickman47]

Hi to all ! I have been given a project to replace an OLD belt drived tachometer with a shaft-mounted encoder. The tach output is 0-10vdc proportional to shaft speed. The signal is then fed to an analog input on the PLC and used to sale welder heat according to shaft speed. My boss wants to use a hollow shaft encoder at 1024 PPR and then convert this signal to 0-10vdc and feed that into the PLC. I have built a board that will do this but I am looking for a module that would be off the shelf. Does anyone know of such a module?

[BobLfoot]

Knowing what flavor of PLC you need to interface with would help tremendously.

[stickman47]

The PLC is a Siemens.

[paulengr]

The S7 series has a built-in high speed counter. You can simply connect the encoder directly to the PLC and get rid of the extraneous and crude analog conversion. Why not go direct? Depending on the speed/resolution you are looking for, the key is either to measure the time interval between pulses or else do pulse counting on a fixed time interval.

[stickman47]

This was my first suggestion since the S7 has the special functions "built in", but management doesn't want to disturb the program. They want to simply replace the existing analog signal with a different device, making the conversion outside the PLC. Dinosaurs still rule the land..

[Ken Moore]

There are numerous signal converters on the market that will convert a freq. signal to a standard analog signal. By using an off the shelf solution you can avoid a lot of head aches. Such as support for the device, spares etc... Just google signal conditioner. Here is a link to just one source: http://www.omega.com/ppt/pptsc.asp?ref=DRF-FR&Nav=vhpf04