MOOGP-I Servoamplifier G122-829A001

Application Notes

1 Scope

These Application Notes are a guide to applying the 

G122-829A001 P-I Servoamplifier. These Application Notes 

can be used to:

 Determine the closed loop structure for your application.

 Select the G122-829A001 for your application. Refer also 

to data sheet G122-829.

 Use these Application Notes to determine your system 

configuration.

 Draw your wiring diagram.

 Install and commission your system.

Aspects, such as hydraulic design, actuator selection, feedback 

transducer selection, performance estimation, etc. are not 

covered by these Application Notes. The G122-202 Application 

Notes (part no C31015) cover some of these aspects. Moog 

Application Engineers can provide more detailed assistance, 

if required.

2 Description

The G122-829A001 is a general purpose, user configurable,

P-I servoamplifier. Selector switches inside the amplifier enable 

either proportional control, integral control, or both to be 

selected. Many aspects of the amplifier’s characteristics can 

be adjusted with front panel pots or selected with internal 

switches. This enables one amplifier to be used in many 

different applications. Refer also to data sheet G122-829.

3 Installation

3.1 Placement

A horizontal DIN rail, mounted on the vertical rear surface 

of an industrial steel enclosure, is the intended method of 

mounting. The rail release clip of the G122-829A001 should 

face down, so the front panel and terminal identifications 

are readable and so the internal electronics receive a cooling 

airflow.

An important consideration for the placement of the module 

is electro magnetic interference (EMI) from other equipment 

in the enclosure. For instance, VF and AC servo drives 

can produce high levels of EMI. Always check the 

EMC compliance of other equipment before placing 

the G122-829A001 close by.

3.2 Cooling

Vents in the top and bottom sides of the G122-829A001 case 

provide cooling for the electronics inside. These vents should 

be left clear. It is important to ensure that equipment below 

does not produce hot exhaust air that heats up the G122-829

3.3 Wiring

The use of crimp “boot lace ferrules” is recommended for the 

screw terminals. Allow sufficient cable length so the circuit 

card can be withdrawn from its case with the wires still 

connected. This enables switch changes on the circuit card 

to be made while the card is still connected and operating. 

An extra 100mm, for cables going outside the enclosure, 

as well as wires connecting to adjacent DIN rail units, 

is adequate.

The screw terminals will accommodate wire sizes from 

0.2mm2 to 2.5mm2 (24AWG to 12AWG). One Amp rated, 

0.2mm2 should be adequate for all applications.

3.4 EMC

The G122-829A001 emits radiation well below the level called 

for in its CE mark test. Therefore, no special precautions are 

required for suppression of emissions. However, immunity from 

external interfering radiation is dependent on careful wiring 

techniques. The accepted method is to use screened cables for 

all connections and to radially terminate the cable screens, in 

an appropriate grounded cable gland, at the point of entry into 

the industrial steel enclosure. If this is not possible, chassis 

ground screw terminals are provided on the G122-829A001. 

Exposed wires should be kept to a minimum length. Connect 

the screens at both ends of the cable to chassis ground.

4 Power supply

24V DC nominal, 22 to 28V

75mA @ 24V without a load, 200mA @ 100mA load.

If an unregulated supply is used the bottom of the ripple 

waveform is not to fall below 22V.

It is recommended that an M205, 250mA T (slow blow) fuse, 

compliant with IEC127-2 sheet 3, be placed in series with the 

+24V input to protect the electronic circuit. If terminal 23 is 

used to power a proportional valve, the fuse should be 

increased to cater for the extra current

Caution

If you intend to use the feedback amplifier adjusted for 

4-20mA, don’t change the feedback gain or zero.

 They are already adjusted for 4-20mA

 To re-adjust for 4-20mA takes a little time, needs test 

equipment and is tedious to do in the field.

6 Input configuration

Inputs 1, 2 and feedback go to the error amplifier and can be 

used for feedback or command. Care needs to be taken in 

selecting signal polarity to achieve negative feedback for 

the overall closed loop. Since the input error amplifier sums 

the signals, the transducer feedback signal needs to be the 

opposite polarity of the command. This can be achieved in 

two ways:

 Arrange for an opposite polarity feedback transducer signal 

and connect it to input 1, input 2 or the positive feedback 

amplifier input.

 If the feedback transducer signal is the same polarity as the 

command, you only have one option: Connect it to the 

negative input of the feedback amplifier.

6.1 Feedback input

An input to the error amplifier: The feedback amplifier is the 

best choice for the feedback signal, for six reasons:

 It leaves input 1 available for command. See 6.2 below.

 It has inverting (negative) and non-inverting (positive) inputs.

 It has zero and gain adjustment pots. This enables a signal 

that does not go to zero volts and has less span than the 

command, to be scaled up to the command. While this is 

not essential, it helps when setting up and trouble-shooting.

 There is a front panel test point for the zeroed and amplified 

signal. This is very convenient (essential) for setting up and 

trouble-shooting.

 There is the option of a plug-in resistor, R16, to give a 

feedback derivative (lead or D) in the output of the feedback 

amplifier.

 It can be set up for a current input by connecting a 240 Ohm 

resistor between terminals 17 and 18 with the 4-20mA 

switch ([SW1:4]).

Default

The feedback amplifier default set-up is 4-20mA flowing into 

terminal 18 and out of terminal 17, producing an output of 

0 to -10V. Reversing the terminals, and hence the current flow, 

will not result in a 0 to +10V output. The feedback zero must 

be adjusted for this arrangement.

Adjusting feedback amp for 4-20mA input and 

0 to -10V output

 Set the feedback gain to minimum (fully counter clockwise). 

The trimpot has 15 turns and will click when minimum is 

reached.

 Connect terminal 17 to terminal 26 (ground).

 Connect the positive of a variable DC power supply to 

terminal 18 and the negative to terminal 26.

 Connect a digital multimeter (DMM), on DC Volts, between 

the front panel feedback amp and ground test points.

 Set the variable supply to 0.96V.

 Adjust the feedback amp zero trimpot until the DMM reads 

0.00V.

 Set the variable supply to 4.80V.

 Adjust the feedback gain trimpot until the DMM reads 

-10.00V.

 Set the variable supply to 0.96V again and check the 

feedback test point is still 0.00V. Trim if necessary and check 

the 4.80V setting again

6.2 Input 1

An input to the error amplifier: This input is ±10V 

non-inverting and has two important features:

 It has a scale pot on its input that enables large inputs to be 

scaled down to match smaller signals on other inputs. Scale 

range is 10 to 100%. Set fully clockwise (FCW), an input of 

100V can match a 10V signal on the other inputs. Note that 

the maximum permissable input voltage is ±95V.

 It has a switch selectable (SW4:2) lag of 55mS that can be 

used to remove transients from the input signal that could 

cause unwanted rapid movement in the output.

Input 1 is well suited to be a command because of these two 

features. If input 1 is used for feedback, be sure the lag is 

switched off. Input resistance after the scale pot is 94k Ohms.

6.3 Input 2

An input to the error amplifier: This input is differential, with 

non-inverting and inverting inputs. It is switch selectable (SW5) 

between 4-20mA and ±10V. The 4-20mA converter produces 

0 to +10V for 4 to 20mA input to terminal 7. R34 connects 

from the output of the amplifier to the input of the error amp. 

It is a plug-in resistor with a default value of 100k Ohms, 

giving a nominal ±10V input signal range when V is selected. 

Input 2 is suitable for command or feedback. R34 can be 

increased to give a larger input range.

Terminal 8, the inverting input, can be connected to ground 

with SW6:1.

6.4 Input 3

An input to the output summing and limiting amplifier via a 

plug-in resistor, R33. A typical use for this input is command 

feed forward or closing the outer loop of a three stage valve. 

With R33 at 10k Ohm, a ±10V input will produce ±100% valve 

drive. Increasing R33 reduces the valve drive.

The summing amp gain can be changed with plug-in resistor 

R27. This is useful if input 3 is being used to close the outer 

loop of a three stage valve.

7 Output configuration

Select the output to match the input requirements of the valve 

(SW2).

 When voltage (V) is selected, ±10V is available into a 

minimum load of 200 Ohm.

 When current (I) is selected, the current level switches 

(SW1:X) enable ±5 to ±100mA to be selected. The switch 

selections sum, so, if for instance 45mA is required, select 

30,10 and 5. The output can drive all known Moog valves 

up to ±100mA. The maximum load at I (Amp) output is:

 RL max = 11V – 39 Ohm

I (Amp)

eg. at 50mA RL max is 181 Ohm

 When 4-20mA is selected, the output V/I switches must be 

in I and the output current SW1 must have switch 3 selected 

for 20mA. Maximum load for 4-20mA output is 500 Ohm.

The output amplifier is limited to approximately 105% of the 

selected full scale output. If both the proportional and 

integrator stages are saturated, the output will not be twice 

the selected full scale but still only 105% of full scale.

8 Step push button

The step push button (SW3) injects -50% valve drive 

disturbance into the output. When released, the valve drive 

reverts to its original level. This feature is useful for closed loop 

gain optimisation.

9 P-I selection

For position closed loops, initially select only P (SW6:2). For 

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 

selectable lag of 55mS.

Input 2: Differential 4-20mA or ±10V, 

switch selectable. 

Connects to error amp via R34. 

±15V max. 

Rin = 390k – ±10V. 

Rin = 240R – 4-20mA. 

R34 is plug-in, 100K (default).

Input 3: Connects to summing amp via R33. 

R33 plug-in. ±10V gives ±100% valve 

drive when R33 = 10k Ohm, ±10% when 

R33 = 100k Ohm.

Feedback input: Differential 4-20mA or ±10V, 

switch selectable. 

±15V max. 

Rin 100k – ±10V. 

Rin 240R – 4-20mA.

Feedback amp: Zero, ±10V. 

Gain, 1 to 10. 

Derivative (velocity) feedback via 

plug-in resistor R16 and fixed capacitor.

Transducer excitation: +10V @ 10mA max. 

Error amp: Unity gain. 

Bias ±1.5V. 

Proportional amp gain: 1 to 20 with R17 = 100k (default). 

Max gain 2000 with R17 = 10M.

Integrator gain: 1 to 45 per second.

Integrator input: Switch selectable from output of unity 

gain error amp or proportional gain amp.

Enable: Relay, +24V @ 8mA, 17 to 32V.

Output amp: Switch selectable voltage, current or 

4-20mA, single ended output, return 

to ground. 

 V. ±10V, minimum load = 200 Ohm. 

 I. ±5, 10, 20, 30, 50mA to a maximum 

of ±100mA.

max load = 11V – 39 Ohm

I (Amp)

 4-20mA. Max load 500R.

Step push button: -50% valve drive disturbance.

Valve supply: Terminal 23, 300mA max.

In position: ±10% of valve drive. 20mA and 40V max 

output to PLC.

Front panel Vs, internal supply – green 

indicators: Valve drive positive – red 

negative – green

Enable – yellow 

In position – green

Front panel Valve ±10V (regardless of output 

test points: signal selection) 

Feedback amplifier output 

signal 0V

Front panel Input 1 scale 

trimpots: Error amp bias 

(15 turns) P gain 

I gain 

Dither level 

Feedback amp gain 

Feedback amp zero

( )

Dither: 200 Hz fixed frequency. 

±10% valve drive. Switch selectable 

on/off.

Supply: Terminal 1, 

24V nominal, 22 to 28V 

75mA @ 24V, no valve current, 

200mA @ 100mA valve current.

±15V output: Terminals 14 and 15, 

± (110mA – max valve current).

Wire size range: 0.2mm2 to 2.5mm2 

(24AWG to 12AWG).

Recommended M205, 250mA T (slow blow) fuse 

supply protection: compliant to IEC127-2 sheet 3. 

If terminal 23 is used to power a 

proportional valve, the fuse should be 

increased to cater for the extra current.

Mounting: DIN rail 

IP 20

Temperature: 0 to +40ºC

Dimensions: 100W x 108H x 45D

Weight: 180g

CE mark: EN50081.1 emission 

EN61000-6-2 immunity

C tick: AS4251.1 emission

19 Internet

www.moog.com/dinmodules