Clamp on Shaft Tach

TheWaterboy · Feb 10, 2015

I need to test 4 vertical pump motors speed. I need to find a tach sensor for each that I can clamp to the shaft and feed to the PLC.

The shaft speed is 1500 rpm and below, VFD controlled. shaft is around 1.25 inches diameter.

I am open to about anything, I will have the cables for these laying on the ground up to the PLC (contrologix) which is about 50 feet away. As I said, its a temporary test.

Is there a sensor ready built for this or will I have to use a prox sensor and hope there is a keyway or bolt to sense?

I would rather clamp a ringlike device to the shaft tha the sensor can reliably pick up, but my googling has not located such a device.

Ideas?

The Plc Kid · Feb 10, 2015

You could use a laser speed tach like this http://www.elovis.de/en/produkte/produkt_2/uspeed.html but it may be more than you want to pay for a temporary setup. Beta Laser Mike and a few others make these also.

shooter · Feb 10, 2015

check if vfd has output.
rpm to PLC is bad choice

The Plc Kid · Feb 10, 2015

You could also use a magnetic encoder but the pickup would need to attach to the rear shaft of the motor. Dynapar makes these.

TheWaterboy · Feb 10, 2015

VFD does have output, I have ordered Ethernet/IP cards to get all the pertenant data from it. But part of this is checking to see if that too is accurate all the time. The pump is not consistent, I suspect its operating right on the egde of its curve and thus becomes a hydraulic issue but I need data to support this before they will bring in the pump engineers. It becomes a design issue (flaw) and so I gotta have all my data right before calling the PE's wrong.

The rear of the shaft is not available on this motor, only the mid part where the coupling and wet seal is located is open.

keithkyll · Feb 10, 2015

Optical sensor with foil tape or white paint mark.
Sensors

Tom Jenkins · Feb 10, 2015

keithkyll said:
Optical sensor with foil tape or white paint mark.
Sensors

+1

Work great, any photo prox will do. You can take the pulse directly into a counter input channel on the PLC or use a converter to get 4-20 mA. I've used the Red Lion versions with success.

TheWaterboy · Feb 10, 2015

Copy that. That was the first thing I thought of since we have a handheld one of those, but mounting was problematic. Considering other options, I guess mounting is the least of my problems.
Think I'll need a high speed module for the input pulse?

a062549 · Feb 10, 2015

Both DynaPar and Turck make shaft clamp tachs/encoders. The also have the m12 style connectors avail.

ASF · Feb 10, 2015

You may not need a high speed input.

1500rpm = 40ms between pulses. If your scantime is low enough you might get away with it.

You also need to make sure that you're not exceeding the maximum input frequency of your digital input, but from memory you can get about 1kHz out of an AB input card, and 1500 pulses per minute is about 25Hz. Take the switching speed of whicever sensor you get into account as well, if it takes 10ms to switch you're going to be pushing the proverbial uphill.

I definitely wouldn't promise it'll work, but if it's for a temporary setup it's definitely worth a shot.

This post on another forum has some detail on a guy doing something similar - he was actually using an encoder and counting pulses from that rather than a sensor, and admittedly he was posting because it wasn't working, but it had worked fine for years before this

MasterBlaster · Feb 10, 2015

Is mounting on a sturdy tripod impractical?

DScott · Feb 10, 2015

How about a mag pickup mounted near the coupling?

sparkie · Feb 10, 2015

TheWaterboy said:
VFD does have output, I have ordered Ethernet/IP cards to get all the pertenant data from it. But part of this is checking to see if that too is accurate all the time. The pump is not consistent, I suspect its operating right on the egde of its curve and thus becomes a hydraulic issue but I need data to support this before they will bring in the pump engineers. It becomes a design issue (flaw) and so I gotta have all my data right before calling the PE's wrong.

The rear of the shaft is not available on this motor, only the mid part where the coupling and wet seal is located is open.

Could you possibly just use a hand tach to check your VFD output? If you have already ordered the gear for coms between the PLC and VFD I would compare your VFD's RPM output to that of a hand tach for accuracy. I would have probably just kept it simple and done this before ordering the com equipment.

Tom Jenkins · Feb 11, 2015

One of the nice things about a photo prox is distance doesn't have to be exact. I usually just bolted a chunk of unistrut to the frame and used a conduit clamp to hold the switch.

osmanmom · Feb 11, 2015

get a DataLogger collect all data for trouble shooting

SP/PV/pressure feedback/speed/amp/hertz

Clamp on Shaft Tach

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