[OMRON] Outputting a number with an analog output

[Bojamijams]

Greetings Gentlemen,

I must admit I haven't worked much with analog output modules outside of controlling a VFD (and that was not in Omron) so this is new to me but I have a puzzle I need to solve.

We have an INT value being passed over ENet from a scale. The scale is in a container that can hold up to 20,000Kg. So it is already a 'scaled' value ready to be worked with in our program.

The customer wants a secondary display in another location that is to display this value. We're using an analog output module (4-20mA) and a large LED display that takes this input to display the value (A RedLion LPAX/MPAX combo unit to be specific)

I've set it up with 3 setpoints. 0mA to show 0Kg. 4mA to show 0Kg (so that when the unit is off it doesn't display a negative value, and a 20mA setpoint that shows 20,000Kg.

Now, the analog unit is a CJ1W-DA041. In CX-Programmer, I get 4mA when I put a decimal value of 0 into this channel. When I put in 4000 I get 20mA. I have a function (basically y=mx+b) that scales this INT value between 0 and 4000.

Here is the problem. The customer wants it accurate to 1Kg. So I need to be able to display 0 to 20,000. But the analog module only has 4000 points between 4mA and 20mA. It would seem the math doesn't work out. Am I missing something due to my inexperience with analog modules or is this simply not possible?

Thanks in advance for any insight!

 

[bernie_carlton]

If they want a 1 in 20,000 part accruacy then every step along the way must have at least that level of accuracy. The accuracy at the end point will be no greater than the least accurate segment.

 

[danw]

If you need a resolution of 1:20,000 then you'll need to find both an output device with that resolution and an input device with that resolution.

- an analog output for the PLC with a D/A with at least 15 bits resolution (32,000 parts unipolar, ±16,000 parts bipolar), which in a practical sense probably means 16 bit resolution

- a display that has 15 or 16 bit resolution.

16 bit resolution is not all that common. You might inquire as to whether Red Lion's display can talk a digital protocol and go that route, because analog has issues of noise and drift issues affect accuracy, even when sufficient resolution is available.

 

[gtsuport]

I have to agree with danw.

I just reviewed the available analog output modules and the best resolution Omron offers is 8000.

You did not indicate how the scale information is being input to the PLC. If it is an analog signal, you need to make sure that resolution is acceptable as well. I only see a couple of modules that meet that requirement.

Hope this will help.

 

[Bojamijams]

Okay that's what I thought. I was being told that resolution is how fast the input can change, not it's total range but even if that were the case, the fact that I only had 4000 total points to work with seemed a limiting point to me.

Gtsupport, I mentioned at the beginning that the scale information is transfered over Ethernet to the PLC as an Int . If it was an analog signal then I would've just passed it along, though would've probably had half the resolution because inputs are at 8000 and I'm still at 4000 on the output side.

But thank you for the confirmation. Looks like we'll need a DeviceNet module for the RedLion display (PLC already has one) and do it that way.

 

[gtsuport]

Sorry missed the Ethernet reference.

DeviceNet master for the CJ would be CJ1W-DRM21.