What is Regulator gain?
What is Regulator gain?
(OP)
Sorry if I am asking a silly question, but what exactly is regulator gain? It is a term at work I keep hearing but I cant place exactly what its supposed to mean. Our product is fuel modules in cars that contain a fuel pressure regulator which opens and dumps excess fuel back into the reservoir, so what would the gain constitute? Thx for any help





RE: What is Regulator gain?
Output signal = Gain * ( E + Td + 1/Ti ∫ E(t)dt ) + Vs
E = Error = Input Signal - Setpoint
Ti = Reset Time
Td = derivative Time
Vs = Bias
The controller then sends the new output signal to the regulator and the regulator moves to a corresponding position.
The output signal strength is effectively the error signal multiplied by the gain setting, so in combination with the derivative and reset times, gain determines both how quickly and how "hard" the regulator responds to any differences between input signal and set point.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: What is Regulator gain?
RE: What is Regulator gain?
RE: What is Regulator gain?
RE: What is Regulator gain?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: What is Regulator gain?
RE: What is Regulator gain?
Mechanical pressure regulators have some amount of 'unbalance' built into them however, which is a function of the poppet seal area, diaphram or sensing area and spring rate. As inlet pressure drops, the outlet 'set pressure' (or the pressure the regulator will hold under constant flow conditions) will increase. This is due to unbalanced forces on the poppet which are opposed by the spring and sensing element.
Do you think this is what is being refered to?
RE: What is Regulator gain?
RE: What is Regulator gain?
RE: What is Regulator gain?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: What is Regulator gain?
In any case the terms are simply the inverse of each other. Gain is the amount of flow through the regulator devided by the error (set pressure-actual pressure). Droop is the error devided by the flow. A larger valve orifice and longer spring (lower spring constant) give you more gain.
RE: What is Regulator gain?
Ref: http://www.fisherregulators.com/technical/tips/
Consider the forces pushing 'up' on a regulator's various internal parts.
1. Upstream pressure times poppet seal area is pushing "up". [1]
2. Downstream pressure times diaphragm/sensing element area also pushes up.
3. Reference force from spring or gas in the case of a dome loaded reg is pushing "down". Note that in the case of a spring, the force down is a function of poppet movement and spring rate. F = k x
Let's disregard changes in upstream pressure for a moment. Downstream pressure pushing up on the diaphram then balances the spring load pushing down. If the poppet is open some amount (dx) and downstream pressure drops, the force up on the diaphram drops and the spring extends which pushes open the poppet to increase flow. But the down force due to the spring is a function of spring rate, so the new opening on the reg is larger but the pressure is necessarily lower by the amount dP = k dx / A. This phenomenon of pressure droping due to the regulator needing to increase flow (increase poppet lift) is known as droop.
Further down on the same page, I see they mention "gain".
So it seems "gain" in this case is being used to indicate the restriction of gas flow to the dome of a pilot operated regulator. I've not heard of this being called "gain" before, but I can understand why after reading that.
I used a spring in the above example regarding droop, but a dome loaded regulator (being called a "pilot operated regulator" by Fisher) is very similar. In the case of a dome loaded reg, the change in dome pressure is also a linear function of sensing element movement. If dome volume is large, relative spring rate is low and droop is minimized. The use of a dome loaded regulator is commonly used where very accurate pressure control is needed over a wide range of flow due to the droop issue. The problem is often that the reg becomes unstable with a very small spring rate.
The way I've seen that typically controlled is isolate the sensing element from downstream pressure and putting an orifice in line. This reduces the volume and increases spring rate, but also allows sensing element pressure and downstream pressure to slowly equilize as gas flows through the orifice which minimizes droop.
Another option is to have a small dome such that the relative spring rate is high. But this means droop is high. Not a very good option.
Another option is to have a small volume on top of the sensing element which has some restriction to flow similar to orificing the sensing pressure. Apparantly, Fischer is calling this "gain". Not sure from reading their definition whether or not increased gain is increased restriction to flow or not though.
~
[1] Note that a balanced poppet minimizes this area and helps reduce set pressure change as upsream pressure changes, but let's disregard this for now.
RE: What is Regulator gain?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com