MOOGP-I Servoamplifier G122-829A001

pressure or velocity loops select I (SW6:4) initially and then P. 

See paragraph 12 below for more detail. For a complete 

discussion of P and I control, see the G122-202 servoamplifier 

Application Notes (part no C31015).

10 Integrator input

The servoamplifier has a unity gain input error amplifier 

followed by two parallel stages, one a proportional amplifier 

and the other an integrator. The outputs of these two stages 

can be switched to the output power amplifier (see paragraph 

7 above) which then drives the valve.

The input to the integrator stage can be switch selected 

(SW4:1) from either the output of the error amplifier, I in = E, 

or the output of the proportional stage, I in = P. The latter 

arrangement is used in the G122-202. It is beyond the scope 

of these Application Notes to detail the benefits of each 

arrangement. If you have experience with the G122-202, 

I in = P would seem to be an easy choice.

11 P only gain

For position loops select only P control (SW6:2). Input a step 

disturbance of 50% valve current with the step push button 

(SW3). Adjust the P gain for the required stability, while 

monitoring the front panel valve test point, or the feedback 

signal. The gain range of the proportional amplifier can be 

moved by changing the plug-in resistor R17. The value loaded 

when shipped is 100k Ohms, which gives a 1 to 20 range. 

Selecting 200k Ohms will give 2 to 40. The circuit will function 

correctly with the value of R17 between 100k Ohms and 

10M Ohms.

Note that as P gain is increased, the movement due to the step 

push button decreases.

12 P and I gains together

If you are inexperienced with integral control the following

set-up method is a good starting point.

 I in = E: Initially select only I (SW6:4). Press the step push 

button (SW3). Increase I gain until one overshoot in the 

feedback signal is observed.

Next select P (SW6:2) and I (SW6:4) together and increase the 

P gain to reduce the overshoot.

For the I in = E arrangement the P and I sequence could be 

reversed. i.e.: adjust P first, followed by I.

 I in = P: For an I in = P arrangement, only the “P followed 

by I” sequence of adjustment can be used.

For a more thorough discussion see G122-202 Application 

Notes (part no C31015).

13 I limit

The contribution from the integrator to the output amplifier 

can be reduced by selecting I limit on (SW6:3). When this 

switch is on the integrator contribution is reduced to 

approximately 15% of the level when it is off. This feature is 

useful in a position loop that may require integral control to 

achieve the required steady state accuracy. The limited integral 

control removes valve null error when the final position is 

reached. It is also useful in a pressure loop to limit overshoot, 

if the valve drive saturates.

14 Dither

The dither frequency is fixed at 200Hz and the level is 

adjustable with the front panel pot to ±10% of valve drive, 

regardless of the type and level of valve drive selected. It can 

be turned on or off with ([SW1:3]). Dither is seldom needed in 

a position loop but can be beneficial in pressure or velocity 

loops. Increase dither until it can just be detected in the 

controlled variable, such as pressure or velocity. Dither can 

compromise valve life, so it should be kept to a minimum.

15 Enable

A relay on the circuit card needs to be energised to connect 

the output stage to its screw terminal and to un-clamp the 

integrator. The clamp prevents integrator wind-up when the 

loop is not operating. Supply 24V to the appropriate terminal 

to energise the relay. The enable switch ([SW1:2]) on the circuit 

card can be set to permanently energise the relay and provide 

a permanent enable.

16 In position

When the valve drive signal falls below ±10% of the selected 

full scale signal, the “in position” signal goes true and provides 

an opto-isolated current path between the + and – terminals. 

This can be connected to a PLC to initiate the next step in a 

control sequence. Do not apply more than 40V to the + 

terminal and ensure the load on the – terminal is less than 

20mA.

The “in position” signal is not relevant for a velocity loop.

17 Withdrawing the circuit card

from its case

The circuit card needs to be withdrawn from its case to set the 

selector switches, change the plug-in resistors and operate the 

step push button.

To do this, push one cover release tab with a pen or 

screwdriver, while gently pulling on the top cover on that side. 

The cover will release approximately one mm. Repeat on the 

second tab on that side. Repeat on the other side and then 

withdraw the cover and circuit card until the required switches 

are exposed. The rigidity of the connecting wires will hold the 

circuit card in position while changes are made.

18 Specifications

Function: P, I, or P & I, switch selectable.

Input 1: Connects to error amp via 94k. 

Scaled to 95V max with switch