Basler Electric Model RA-70 Microprocessor-Based Reference Adjuster

The Basler Microprocessor-Based Reference Adjuster, Model RA-70. replaces Motor Operated

Potentiometers and provides a totally solid-state method of adjusting the setpoint on Basler Automatic

Voltage Regulators (AVRs), Basler Shunt Static Exciter-Regulators (SSEs), Basler Manual Voltage

Controls (MVCs), the Basler Var/Power Factor Controller (SCP-250) and other input devices having a

rheostat or potentiometer type control adjustment. The unit is designed for "behind-the-panel" mounting in

switchgear or control boxes. All controls, inputs, outputs, and LED indicators are located on the unit's

front panel for ease of installation and adjustment. The RA-70 Reference Adjuster also comes equipped

with a 0-1 mA output signal to operate a position indicator that will indicate the setpoint position.

The Reference Adjuster is completely compatible with the following Basler equipment:

• Shunt Static Exciter-Regulator (SSE), both for automatic and manual adjust functions

• SSR series of Voltage Regulators

• SR-A, SR-E, SR-H, and SR-F series of Voltage Regulators

• APR series of Voltage Regulators

• AVC63-12 and AVC125-10 Voltage Regulators

• MVC-112. MVC-236. and MVC-301 Manual Voltage Controls

The Reference Adjuster is capable of being interfaced with the above listed items and with the following

Basler system control devices:

• Minimum/Maximum Excitation Limiter (EL-200)

• Var/Power Factor Controller (SCP-250)

• Underfrequency/Overvoltage Module (UFOV-260)

The Reference Adjuster can be used for almost any application where rheostat or potentiometer output is

required.

1. For a rheostat output, match the ohmic output from the Style Chart (Figure 1) for the RA-70A

model.

2. For a potentiometer output, match the ohmic output from the Style Charts (Figures 2 and 3) for

the RA-70M or RA-70P models.

Style Charts

The complete model number of the Reference Adjuster is a combination of letters and numbers indicating

the features which are included. Figure 1 is the style chart for Reference Adjusters Having a Voltage

Regulator Interface. Figure 2 is the style chart for Reference Adjusters having a Manual Voltage Control

Interface. Figure 3 is the style chart for Reference Adjusters having a VAR/Power Factor Control

Interface. For example, a Reference Adjuster used with a Voltage Regulator may have a model number of

RA-70 A SC1R. This RA-70 would have the following features:

A) A voltage regulator interface is used

S) 24 Vdc is used for input power

C) The control input is 4 - 20 mA

1) The type of voltage regulator - SR-F, SR-E/H, SSE

R) Dual reference signals are output for twin AVRs

Power Supply Circuit

The power supply is available in two different styles. The Type S power supply has a single source input

which accepts only 24 Vdc. The Type D power supply has a dual input (redundant) which accepts both

125 Vdc and 120 Vac simultaneously. Thus, with a Type D power supply, if one of the two input voltages

should fail, the reference adjuster will remain operational by using the other input voltage. Both types of

power supplies provide all the internal operating power for the reference adjuster. Refer to the

Specifications chapter for the input power requirements.

Output Circuits

This circuit provides the necessary control resistance to the various devices that the reference adjuster

will control. Depending upon the type of application, the output will simulate a two-wire rheostat or a

three-wire potentiometer. Refer to the style charts in the Introduction chapter for values and applicability.

Metering Output Circuits

These circuits provide the drive voltage or current to a remote position meter. See the Installation chapter

for meter part numbers, mounting, and interconnection information.

Pre-Positioning Function

The reference adjuster provides a pre-position capability (i.e.: automatic return to the pre-set value of

resistance). The Pre-Position function can be programmed to hold the reference adjuster output to a pre

programmed value while ignoring all raise/lower inputs until the Pre-Position function is turned off. The

Pre-Position function can also be pre-programmed to allow the raise/lower inputs to control the reference

adjuster output only after the pre-position setting has been attained.

RA-70M Theory of Operation

The RA-70M operates in a similar manner to the RA-70A and RA-70P. The basic differences are that the

RA-70M is designed to provide a three-wire potentiometer compatible output and is used in conjunction

with the Basler Manual Voltage Controls to provide an autotracking capability for "bumpless" transfer

between the Auto and Manual operating modes of many exciter systems. A diagram showing the RA-70M

function blocks is shown in Figure 5.

Nulling/Autotracking Input Circuits

This sensing circuit connects to the F+ and F− outputs of the AVR and to the F+ and F− outputs of the

MVC. Both inputs are compared and the difference is sent to the microprocessor for processing and

output as the nulling signal. If Autotracking is enabled, the null output will read zero as long as tracking is

maintained. The field voltage range (32 Vdc, 63 Vdc, or 125 Vdc) is automatically selected. A front panel

LED lights whenever the AVR and MVC are nulled.

Pushbutton/Contact Inputs Circuit

The pushbuttons (front panel switches) provide for front panel control over the Raise, Lower, Pre-position

1. Pre-position 2. Mode Select, and Programming functions. External dry contacts provide the same

functions as the first four pushbuttons on the front panel except for the Programming function, which is

available only by the use of the front panel pushbuttons. The contact inputs allow remote control of the

reference adjuster.