The key feature of the Dold Speed Monitoring Relays is that they are super easy to configure
and use.
Given one or two proximity sensors in, it can be set up to monitor overspeed, under
speed, speed inside a window or speed outside a window.
Let’s setup one for overspeed monitoring.
There are wiring diagrams for each case in the user manual.
Here is how I wired my little demo station.
First, I’m only using one NPN Proximity Sensor, so I just wired it to
both inputs.
Whether you need one or two sensors here will depend on your system's needs.
Just know that you have the flexibility to do either
with this speed monitoring relay.
The voltage and grounds are tied together inside the unit,
so we don’t have to replicate that wiring here.
The relay is controlling the contactors like this and monitoring their aux contacts like
this.
We’ll use auto reset in this first example so we don’t need a push button here.
The contactors are wired in series between the motor and the variable frequency drive
which I’m using to control the motor speed.
Here’s my little test setup with the part numbers I’m using in this demo.
Notice that the proximity sensor only detects this single hole each rotation.
So, the speed monitor will see just a single pulse per revolution.
Well great!
I’ll apply power to the speed monitor and press a button to wake up the
display.
Press the right button and then the left button to change parameters.
Get through all the various self-test and display messages.
The Power LED flashes green to remind you that
you are in parameter entry mode.
If it flashes RED, then something is wrong with the parameters.
We can change the parameters, the display language, do a factory reset, activate change
tracking and see the Dold contact info.
We want to change the parameters, so I’ll scroll back up to that and hit OK.
What function do we want?
We want overspeed detection.
What do we want our overspeed frequency limit to be?
How about 10 revolutions per second?
This is important, since our sensor is only generating a single pulse each revolution
we just put a 10 here.
What if we were using this sensor that sees the 36 sprocket teeth
pass by every rotation?
Well, since the speed monitor will see 36 pulses per revolution,
and we want 10 revolutions per second, we would need a 360 here.
That’s important to understand – the speed monitor isn’t
really monitoring motor speed here, it’s monitoring pulses per second.
If you remember that, you’ll be in good shape.
We can change the hysteresis, various time delays, and alarm handling.
We didn’t connect a manual reset button, so we’ll go with
automatic alarm reset.
Let’s get back to the top-level menu ... and that’s it!
Hit this guy to exit the menu system.
And acknowledge we made these changes.
The power LED is solid, so we know we ae not in parameter entry mode and we see the K1/K2
LED is lit.
That tells us the contactors are enabled right now.
This is the Error LED and this one lights up when timing delays expire.
This chart in the user manual explains all of these and what the various flashing patterns
indicate.
We see the current shaft speed is less than .75Hz because the motor isn’t spinning.
If I turn the motor on, then we see the frequency of the pulses coming into the speed monitor,
which in this example is just one pulse per revolution so we are seeing the actual shaft
speed.
I’ll increase the motor speed up past our 10 Hz cutoff and … uh oh … what’s
going on.
My system is freaking out.
We see the contactors are turning on and off over
and over again.
What’s going on?
Well, we increased the motor speed to exceed the cutoff, so the speed relay opened the
contactors to kill power to the motor.
When the motor slows down enough, the speed monitoring
relay automatically resets because we told it to and it closes the contactors.
The motor ramps back up past the frequency limit, so
the speed relay cuts the motor off again, resets again, enables the motor again, etc.
So, we’re stuck in this reset loop.
If I slow the motor back down, then everything gets back to normal.
So, the issue is the automatic reset is sending us right back into the fault mode.
Let’s turn the motor off while we fix this.
Let’s hold these two buttons down again to get back to the menu, work our way down
to parameters … alarm memory … and switch to alarm memory, which requires a manual reset,
and hit OK.
I’ll back out of here until I see the confirmation screen.
It’s reminding me I changed something; we know that, so
I’ll hit OK and we are back to the main screen.
I added a momentary pushbutton like this.
Now if I increase the motor speed as soon as it hits 10Hz, or really 10 sensor pulses
per second, the speed relay opens the contactors and shuts the motor down.
But this time without automatic reset, it stays there.
I’ll reduce the motor speed, then press reset and the
motor is back up and running.
Exactly what we expect.
The key thing to remember is this speed you see here isn’t rotations per second – it’s
the number of pulses per second the speed relay sees.
Since we only had one pulse per revolution, it also happens to be the rotation
rate in Hz.
So the bottom line is, you are entering the frequency of the incoming pulses in Hz.
I love how easy this is to set up and that I can see at a glance exactly what configuration
I have without having to decode a bunch of jumpers or dip switches.
And since it uses digital NPN or PNP inputs, you don’t
have to spend a lot of time calibrating or tuning analog inputs.
That saves you a lot of time and frustration and just makes your
system more reliable and stable.
And since there is no restriction on current draw of the proximity sensor, you aren’t
limited to a proximity sensor.
You could use a contrast sensor, an optical sensor or pretty
much anything you want that has a standard NPN or PNP output.
Well, that ought to be enough to get you up and running.
Click here to learn more about the Dold Speed Monitoring Relay.
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