red lion PRA2 User Manual

7

8

9

10

11

12

6

5

4

3

2

1

2.37 (60.2)

1.77

(45.0)

SOCKET P/N 2300200

(ORDER SEPARATELY)

.88

(22.4)

4.44

(112.8)

* RANGE ADJUSTMENT (VOLTAGE & CURRENT OUTPUT)

.84

(21.3)

2.69

(68.3)

2.31 (58.7)

.84

(21.3)

SOCKET
P/N 2300200

.16 (4.1) DIA.

2 HOLES

* ZERO ADJUSTMENT (CURRENT OUTPUT ONLY)

* 20 TURN SCREWDRIVER
ADJUSTMENTS ACCESSIBLE
THROUGH TOP

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MODEL PRA2 - PULSE RATE TO ANALOG CONVERTER

 DELIVERS ANALOG OUTPUT PROPORTIONAL TO INPUT

PULSE-RATE (FREQUENCY)

 ACCEPTS VARIABLE PULSE-RATE INPUTS FROM A WIDE

VARIETY OF SENSORS

 DUAL SIGNAL OUTPUT, 0 TO 10 VDC PLUS SELECTABLE

SIGNAL CURRENT OUTPUT OF 0 TO 1 MA OR 4 TO 20 MA

 SELECTABLE FREQUENCY RANGE RATINGS FROM 30 HZ TO

10 KHZ
 ACCURACY (LINEARITY) 0.25%
 SWITCH SELECTABLE FOR 115 OR 230 VAC

Bulletin No. PRA2-C
Drawing No. LP0540
Released 10/12

DESCRIPTION

The Model PRA2 is a convenient plug-in module that provides voltage and

current analog output signals proportional to the pulse-rate (frequency) of the
input signal. In typical applications the PRA2 input is supplied by a machine
mounted sensor that generates a signal which has a frequency proportional to
machine or process speed. The PRA2 converts the frequency content of this
signal to analog form for operating chart recorders, supplying speed control
signals, or driving other controls and indicators that require analog input.

The PRA2 develops an internal “constant-area” pulse from the negative

going edge of each input pulse or wave form cycle. These “Constant-area”
pulses are fixed in voltage amplitude and time duration. The PRA2 then takes
the average of a train of these pulses to generate an output voltage level
proportional to the frequency. Another circuit within the PRA2 monitors the
voltage output and produces a current output signal that will deliver either 0 to
1 or 4 to 20 mA, as determined by a set-up switch.

This unit is available with five overlapping adjustable range ratings, each
rating providing a calibration adjustment to deliver maximum output over an
input frequency range of approximately 3.3:1. Since the PRA2 develops an
output by averaging pulses, an inherent response time is involved (See response
table, next page). The minimum response time is fixed for each range rating. It
is longest for the lowest range rating and decreases as the frequency range rating
increases. Response time must be considered, when using the PRA2 to provide
closed-loop speed feedback signals, to avoid stability problems. For speed
feedback applications it is usually advisable to select a high frequency range
coupled with an appropriate sensor arrangement that delivers a high pulse rate.

The internal output filtering supplied for averaging purposes is kept to a
minimum to provide the fastest practical response time for each range rating.
Extra external capacitance can be added to provide more filtering if required.

DIMENSIONS In inches (mm)

The plug-in module mates with a heavy duty, CSA approved base mounting

socket with pressure clamp screw terminals that accept stripped wires without lugs.

SPECIFICATIONS

1. PRIMARY SUPPLY VOLTAGE: Switch selectable for 115 or 230 VAC

±10%, 60 Hz; 8 VA

2. SENSOR OUTPUT POWER: +12 VDC ±5% regulated, 60 mA max.

3. SIGNAL INPUT CHARACTERISTICS: See “Input & Output Switch

Set-up” section.

4. MAX. FREQUENCY ADJUSTMENT: 30 Hz to 10 KHz

5. SIGNAL VOLTAGE OUTPUT: 0 to 10 VDC @ 10 mA max.

6. SIGNAL CURRENT OUTPUT (Selectable):

0 to 1 mA into load resistance range 0 to 4 K.
4 to 20 mA into load resistance range 0 to 250 

7. LINEARITY: ±0.25% of full range setting.

8. VOLTAGE/CURRENT OUTPUT TRACKING: Current Signals follow

voltage signals within ±3% of full range setting.

9. RESPONSE TIME: See table on next page.

10. OPERATING TEMPERATURE RANGE: 0 to 60

o

C.

11. WEIGHT: PRA2 - 8 oz (226.8 g); Mating 12-Pin Socket - 2 oz (56.7 g).

ORDERING INFORMATION

MODEL NO. DESCRIPTION PART NUMBERS

PRA2 Pulse Rate to Analog Converter PRA20000



Socket, 12-Pin 2300200

1

7

8

9

10

11

12 1

2

3

4

5

6

INPUT

N.C.

COMM.

+12V

TO

SENSOR

A.C.

POWER

(SEE PG. 3)

0-10 VDC

AT 10MA MAX.

OUTPUT

OPTIONAL

FILTER CAP

(-)

(+)

CURRENT
OUTPUT
0-1MA, MAX. R = 4K
4-20MA, MAX. R = 250Ω

L

L

R

L

COMM. COMM.

N.C.

(-)

APPLICATION CONSIDERATIONS

OVER­RANGE

OUTPUT SATUATION

OUTPUT CURRENT 4-20MA

OUTPUT CURRENT 0-1MA

OUTPUT VOLTS

LINEAR REGION

0123456

4

0

12

.5

20

1

510

ADJUSTABLE

RANGE

FREQUENCY KHZ

TRANSFER CHARACTERISTICS
FOR RANGE 4
(FULL SCALE ADJUSTMENT
RANGE, 1 - 3 KHZ)

FULL SCALE OUTPUT

MINIMUM RANGE

MAXIMUM RANGE

10% 20% 40% 60%

0

1

2

% OF FULL SCALE OUTPUT

3

80% 100%

TYPICAL OUTPUT RIPPLE

(SEE TABLE FOR CURVE KEY

TO PARTICULAR PRA2 RANGE)

MIN. FULL SCALE ADJUSTMENT

MAX. FULL SCALE ADJUSTMENT

PEAK TO PEAK RIPPLE VOLTS

A

B

C

C

B

A

0

3456

43 65

43 65

43 65

43 65

12

12

12

12

21

21 43

12 346556

21 43 65

12 34

21 43

56

65

ON ON

**

**

**

**

**

**

**

**

**

**

CONNECTIONS & SET-UP ADJUSTMENTS

+

(+)

VOLTAGE OUTPUT ADJUSTMENT:

Only the RANGE ADJUSTMENT is effective when voltage output is used.

(Zero Adjustment affects only current output.)

PROCEDURE

1. Set AC power switch to proper position.

2. Connect voltmeter to Terminals 10 & 12.

3. Set the Range Switches for desired max. input frequency.

4. Apply the maximum input frequency and turn the *RANGE
ADJUSTMENT to obtain the desired output voltage.

ADJUSTABLE RANGE RATINGS & OVER RANGE OPERATION

Frequency Range

RANGE

FULL SCALE

ADJUSTMENT

1 30 Hz to 100 Hz

2 100 Hz to 300 Hz

3 300 Hz to 1 kHz

SW1

SW2

CURRENT OUTPUT ADJUSTMENTS:

When current output is used, the ZERO ADJUSTMENT must be set before

RANGE ADJUSTMENT setting is attempted.

PROCEDURE

1. Set AC power switch to proper position.

2. Select current range with switch SW2-6 (OFF 0-1 mA / ON 4-20 mA) .

3. Connect a milliammeter in series with the current loop circuit from Term 1

to Term 3. CAUTION: DO NOT exceed maximum load resistance specified
for the current range.

4. Set the Range Switches for desired max. input frequency.

5. Zero Adjustment:
A) 0-1 mA Range - With input signal removed (zero frequency) turn ZERO

B) 4-20 mA Range - Set ZERO ADJUST until current is 4 mA.

6. *Range Adjustment: Apply maximum frequency input signal and set
RANGE ADJUSTMENT to get desired output.

* RANGE ADJUSTMENT - Turning CW decreases output at a given frequency

(increases range) and turning CCW increases output (decreases range).

and the output voltage or current will be proportional to input frequency. If the
input frequency exceeds the full-scale range setting (over range), the output
will flatten out and saturate at some level above 10 V at all higher frequencies.

CAUTION: Maximum input frequency for PRA2 modules is 10 KHz. At input

frequencies in excess of 10 KHz, the frequency roll-off characteristics of the
input circuit will cause signal dropout and result in discontinuous
operation.

ADJUST CW until positive current flow is indicated. Then, turn back
CCW until the current flow just reaches zero. Stop turning the adjustment
at that point.

4 1 kHz to 3 kHz

5 3 kHz to 10 kHz

Frequency Curves

The Transfer Curve (at right) shows the frequency-input/voltage-output
relationship for the PRA2, Range #4 for both Min. Range (0-1 KHz) and Max.
Range (0-3 KHz) adjustment. These curves are typical and apply to all PRA2
ranges.

As shown by these curves, the PRA2 RANGE ADJUSTMENT allows the
unit to be calibrated to deliver full scale output for any input frequency from
the min. to max. range ratings. As long as the input frequency is equal-to or
less-than the full-scale range setting, the PRA2 is operating in its linear region

OUTPUT RESPONSE & RIPPLE CHARACTERISTICS

PRA2 Modules are supplied with a minimum amount of output ripple
filtering in order to avoid compromising response-time. The data presented
below, permits a reasonable estimate of the amount of ripple and the response­time that will be experienced in a particular application. As shown by the
curves below, the amount of output ripple depends on the range setting and the
input frequency.

Ripple voltage can be reduced by adding external filter capacitance, but
ripple-reduction is a trade-off against increased response times. This must be
kept in mind, especially if the PRA2 is to be used to supply feedback control
signals.

The values of capacitance given in the table are for reference only and do
not imply a limit to the amount of capacitance that can be added. For example,
an external filter capacitance may be 10 times the reference values shown for
a very high degree of ripple reduction, provided that the resulting long
response time is acceptable.

RANGE

FULL SCALE RANGE

ADJUSTMENT

MIN MAX [1] [2] [3]

1 30 Hz 100 Hz 250 msec A 2.2 mfd
2 100 Hz 300 Hz 75 msec A 0.56 mfd
3 0.3 KHz 1 KHz 25 msec A 0.22 mfd
4 1 KHz 3 KHz 10 msec B 0.1 mfd
5 3 KHz 10 KHz 8 msec C 0.047 mfd

RESPONSE

TIME

RIPPLE
CURVE

EXT CAP (REF)

Note: If large capacitor values are required to achieve a high degree of ripple

reduction, tantalum capacitors rated at 35 V or more are recommended.

(Proper polarity must be observed. See Connection Drawing above.)

[1] RESPONSE TIME - Time required for the output to reach 90% of final value

when the frequency is instantly changed from 0 to full-scale range frequency.
[2] See “Typical Output Ripple” Curves (at left).
[3] External Capacitance can be added between terminals 10 and 11 to decrease

ripple. Reference values shown in MFD, will reduce ripple approximately 50%

and will roughly double response times.

2