MOOG P-I Servoamplifier G122-829A001

MOOG P-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 elctronics 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 Allow sufficient cable length so the circuit card can be withdrawn from its case with the wires still connected.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.

5 Set-up adjustments

To access the circuit card switches, the circuit card must be withdrawn from the case. See paragraph 17.

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.

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 14 Dither 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.