Dwyer 3000SGT - Manual (Page 4)

Voltage Input
The PHOTOHELIC
® SGT can easily be adapted for receivers requiring 1-5 VDC
input. Insert a 250 ohm, 1/2 watt resistor in series with the current loop but parallel
to the receiver input. Locate this resistor as close as possible to the receiver input.
Because resistor accuracy directly influences output signal accuracy, we
recommend use of a precision ±0.1% tolerance resistor to minimize this effect.
Transmitter Output Calibration
Each unit is factory calibrated to produce 4mA DC of loop current at zero pressure
and 20mA DC at full scale. To check calibration use the following procedure.
1. Connect a controllable source of pressure to the high pressure port and leave
the low pressure port vented to atmosphere.
2. With transmitter connected to its companion receiver and power supply, insert
an accurate milliammeter ranged to approximately 30 mA in series with the
current loop.
3. Apply electrical power to the system and check for proper operation. Slowly
apply pressure and confirm that loop current increases above the 4 mA zero
pressure value.
4. Span and zero controls are located behind the terminal board as shown in
Figure L. Apply pressure until gage reads full scale and adjust span control for
20 mA loop current.
5. Relieve pressure and adjust the zero control for a reading of 4 mA loop current.
6. Zero and span controls are slightly interactive so steps 4 and 5 should be
repeated until outputs are consistently 4 and 20mA, respectively.
7. Remove the milliammeter from the current loop, make connections to system
pressure sources and place unit in service.
Multiple Receiver Installation
An advantage of the standard 4-20 mA DC output signal used in Series 3000 SGT
switch/gage/transmitters is the compatibility with a wide range of receivers. Devices
such as the A-701 Digital Readout, a chart recorder and other process control
equipment can all be operated simultaneously. It is only necessary that all devices
be designed for a standard 4-20 mA DC input, the proper polarity of input
connections be observed and the combined receiver resistances not exceed the
maximum for the current loop. If any receiver indicates a negative or downscale
reading, the signal input leads are reversed.
Maintenance
After final installation of the PHOTOHELIC
® SGT no routine maintenance is
necessary. A periodic check of calibration is recommended following the procedure
under TRANSMITTER OUTPUT CALIBRATION. Otherwise, these units are not
field repairable and should be returned, freight prepaid, to the following address if
service is necessary. Be sure to include a brief description of the problem plus any
relative application information available.
Dwyer Instruments, Inc.
Attn: Repair Department
102 Highway 212
Michigan City, IN 46360
SERIES
3000 SGT
PRESSURE
TRANSMITTER RECEIVER
POWER
SUPPLY
10-35 VDC
SPAN ZERO
Figure J
Figure L
MAXIMUM VALUE (1250Ω)
RL MAX. = Vps-10.0
20 mA DC
OPERATING
REGION
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
50
T
O
T
AL RECEIVER RESIST
ANCE (
Ω
)
0 5 10 13 15 20 25 30 35 40
VDC
NOTE: RECEIVER MAY BE IN SERIES WITH
+ OR - LEG OF CONTROL LOOP
©Copyright 2010 Dwyer Instruments, Inc. Printed in U.S.A. 12/10 FR# 13-440202-05 Rev.3
Figure K
DWYER INSTRUMENTS, INC.
P.O. BOX 373 • MICHIGAN CITY, INDIANA 46361 U.S.A.
Phone: 219/879-8000 www.dwyer-inst.com
Fax: 219/872-9057 e-mail: [email protected]
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