Ramp Generator 1

[TugboatEng]

I'm looking for a device that I can mount online of a 4-20mA control signal that delays rising values. The closest item I can come up with is a ramp generator but that only ramps up from step. I need it to slow a rising input. This is to limit engine acceleration rates to reduce smoking of a diesel engine.

 

[IRstuff]

Seems to me that a ramp generator is as good as using a 555 for delay. You start the ramp and trigger a response when the ramp crosses a desired threshold and you control the delay by the speed of the ramp.

Or am I misinterpreting your post?

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[Heaviside1925]

OP,
Is this only to delay the rate of rising or to delay the response all together? What device is supplying the 4-20 and what device is it controlling? There are signal conditioners that might work, there are even some with built in PID functionality, depending on how conditional your requirements are for control as small plc may be needed.

Edit: For other seeking information from this thread, I would normally not just throw out a PID controller for someone not familiar with the control theory behind them, but the OP has demonstrated a high level of competence in many areas though other posts that he's answered, so I do not think a quick dive into tuning PID loops would be out of their grasp.

 

[waross]

Hang a capacitor on it Tug.
You may need a capacitor/resistor combination.
With a resistor you may calculate the time constant.
The RC time constant, denoted τ (lowercase tau), the time constant (in seconds) of a resistor–capacitor circuit (RC circuit), is equal to the product of the circuit resistance (in ohms) and the circuit capacitance (in farads), i.e.:

It is accepted that it takes 5 time constants to stabilize.
A one second time constant will ramp over five seconds.

Choose a value of resistor that will shunt current away from the load, acting as a resistor in parallel.
The first time constant will increase to 63% of the change in value, so quite quick for the first time constant.
The remaining 37% will be spread over the remaining five time constants.

Not as good as a ramp circuit but very economical.
All changes in throttle setting will be subject to the delay.
That is both increasing and decreasing throttle commands.
Then there is the old school mechanical solution.
A slip joint on the actuator retarded by a dash pot.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[FacEngrPE]

Look at proportional controls that have a gain adjustment. Lower gain results in slower ramp, but increases undershoot. Yes you can tune a PID controller to do this.

waross suggests the same thing in discrete components. Adjust gain by changing the R and C values.

 

[TugboatEng]

Heaviside, the signal is output from an azimuthing stern drive for a boat. It passes straight to the engine control module. The signal represents the angle of the throttle handle.

I have the ability to set the ramp in the engine ECM but I can't set the up and down ramps independently.

The Z-drive also has ramp tables but I have to hire the manufacturer to program this on multiple units in multiple locations. $$$.

Waross, I like your idea but I think I need more control. The governors on these engines operate as constant speed governors so it doesn't take much difference between set and actual speeds to trigger a very large throttle output. I can adjust gain settings on the governor but things get very sluggish.

I was hoping to find a module from a commercial company like Phoenix Contact with dip switch programming so it can be installed by unskilled individuals.

 

[Heaviside1925]

OP,
Thank you for the additional information, it's in line with what I was suspecting. Let me do some digging. In the mean time, I wouldn't give up on waross's suggestion just yet. Since this is a rate issue, how fast the throttle is moving, is it possible to use a dashpot to slow the rate?

 

[Heaviside1925]

OP,
After rereading your response, I don't know of an off the shelf for directional rate control like you are seeking. Outside of a mechanical solution, I would use a small plc with your AI from your Z-drive and AO to your ECM, with the logic: a comparator to determine positive or negative rate, If positive set a max timed ramp function, If negative allow the signal 1:1. In leu of a ramp function a PID loop could be used with your gain determined by the polarity of the rate comparator. I am recommending a PLC because they are my go to for issues like this but about any programmable controller that allows these functions can be used.

 

[3DDave]

Gotta love vendor lock-in.

 

[TugboatEng]

Did I say "must be" or did I say "like"? My engine supplier uses PC components for their controls. That is why I mentioned their name.

 

[danw2]

The Honeywell UDC2800 is a PID single loop controller. It has a control output rate limiting function which limits the maximum rate of change of the controller output.

The output rate limit is configured separately for upscale rate or downscale rate. The parameter setting is a whole number, percent of output per minute.

It can be configured so that the output tracks the input. To do this, you'd need the basic controller with the universal input with a 250 Ohm resistor for the 4-20mA input. DC2800-Cx-xS0-200-xxx-0x-x

- wire the 4-20mA signal into Input 1 using a 250 Ohm resistor, configure Input 1 for 4-20mA, linear, range 0.0-100.0, minimum filter, ratio = 1.0, bias = whatever to trim the offset between your signal and UDC,

- to get proportional only control, use control algorithm = PD+Manual Reset (Proportional-Derivative Plus Manual Reset), and configure both the derivative and integral values to zero in the Tuning group.

In the Control group,
PV Source = Input 1
PID Sets = 1
local SP = 1
Remote SP source = None
SP Tracking = None
Power up Mode = Auto/Local SP
SP High Limit - 0.0
SP Low Limit = 0.0 (locks SP at zero)
Action Direction = Direct
Output Rate = enable
Rate up % per Min = X
Rate down % per Min = 0 (no effect)
Output High Limit = 100
Output Low limit = 0
Preset Manual output = X (output on power-up)
Proportion unit = PB or Gain

- In the tuning group, set Gain = 1 (or PB = 100)
- in operational mode, make sure SP1 = 0.00 (critically important)

In direct action, PB=100, with an SP = 0.0, the output will track input signal over the range of 0-100.

With the output rate limit enabled for rate upscale, the output lags the input by whatever limit factor is entered. Downscale output is unaffected.

The "Lower Display" key puts the Output value (%) in the lowest display

I'm suggesting locking the setpoint at 0.0 by configuring the SP high as 0.0 and SP low as 0.0 so the SP can't be changed from the keypad. The auto/manual key can be disabled in the setup to prevent the controller from being 'popped' into manual mode "accidently" (oh, is that what that does . . . )

 

[TugboatEng]

I don't think the ambient temperature limits of that unit are acceptable. Having worked in larger engine rooms, the control cabinets or control rooms were refrigerated. We don't get that luxury on small boats. To ensure long component life, I like to see temperature ratings of 60°C+.

 

[catserveng]

Tug,

Been where you're at more than a few times.

Are you doing a single vessel or multiple?

If multiple vessels, are they the same design, displacement and doing the same type work?

For a one off, a micro PLC designed for machine tools is probably the best solution, especially for the first try, at least in my experience. I have been using the Allen Bradley Mirco 850 series in similar situations last few years, the seem to stand the rigors of harsh environments better than most I've tried, temp range is -20 to +65 C, the "free" software works ok, except can't do online edits.

For multiple units I'd contact Axiomatic,

https://www.axiomatic.com/

They build a lot of different modules for signal conditioning and conversion, and if they don't have exactly what you need they have been very helpful in providing a solution. I have used their stuff extensively on engine swaps and emissions retrofits on Gen set, industrial units and heavy construction and mining equipment. For me their customer service has been exceptional and their products have provided me excellent service. If you look thru their website you may recognize modules they sully to many engine manufacturetrs.

If you'd like to discuss further directly use the info email at the website below.

Good luck!
MikeL

http://www.pactectric.com

 

[TugboatEng]

At this point we're looking at a single vessel. We are doing some repowers this year and I want to be prepared for more. There are a few different hulls but many of the one that is causing trouble.

The smoke limitations are not allowing the engine to exceed the prop curve. Off to the pump forum for the next question.