Dwyer 605 - Manual (Page 3)

ELECTRICAL CONNECTIONS
CAUTION: DO NOT EXCEED SPECIFIED SUPPLY VOLTAGE RAT-
INGS. PERMANENT DAMAGE NOT COVERED BY WARRANTY WILL
RESULT. THIS UNIT IS NOT DESIGNED FOR AC VOLTAGE OPERA-
TION.
Electrical connections to the Series 605 Transmitter are made to the
two-screw terminal strip on the rear of the case. Polarity is indicated by
+ and – signs stamped on side. The schematic diagram of the Series
605 transmitter is illustrated in Figure B.
An external power supply delivering 10.0 to 35 VDC with a minimum cur-
rent capability of 40 milliamps must be used to power the control loop in
which the Series 605 transmitter is connected. Refer to Fig. B for con-
nection of the power supply, transmitter and receiver. The range of
appropriate receiver load resistances (RL) for the power supply voltage
available is given by the formula and graph in Fig. C. Shielded two wire
cable is recommended for control loop wiring and the negative side of
the loop may be grounded if desired. Note also that the receiver may be
connected in either the negative or positive side of the loop, whichever
is most convenient. Should polarity of the transmitter or receiver be
inadvertently reversed, the loop will not function properly but no damage
will be done to the transmitter.
SERIES 605
PRESSURE
TRANSMITTER
POWER
SUPPLY
10.0-35 VDC
RECEIVER (RL)
SEE FIG. C
NOTE: RECEIVER MAY BE IN
SERIES WITH + OR -
LEG OF CONTROL LOOP
The maximum length of connecting wire between the transmitter and the
receiver is a function of wire size and receiver resistance. That portion of
the total current loop resistance represented by the resistance of the
connecting wires themselves should not exceed 10% of the receiver
resistance. For extremely long runs (over 1,000 feet), it is desirable to
select receivers with higher resistances in order to keep the size and
cost of the connecting leads as low as possible. In installations where
the connecting run is no more than 100 feet, connecting lead wire as
small as No. 22 Ga. can be used.
The Series 605 transmitters can be used with receivers requiring 1-5 volt
input rather than 4-20 mA. If the receiver requires a 1-5 volt input, insert
a 250 ohm, 1/2 watt resistor in series with the current loop but in paral-
lel with the receiver input. Referring to Figure B, RL becomes the 250
ohm resistor and point X and Y are connected to the receiver input, point
X being positive (+) and point Y negative (–) or ground. The resistor
should be connected at the panel end of the transmitter current loop
close to the receiver input to take advantage of the immunity of the cur-
rent loop to electrical noise pickup. Most electronic component distribu-
tors stock a 249 r, 1/2 watt, ±1% tolerance metal film resistor which is
adequate for this application.
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0 5 10 15 20 25 30 35 40
RECEIVER RESIST
ANCE R
L
(Ω
)
POWER SUPPLY VOLTAGE - VDC
RL MAX = V PS - 10.0V
20 mA DC
MAXIMUM VALUE (1250)
OPERATING
REGION
OUTPUT RANGING
Each Series 605 Magnehelic ® indicating transmitter is factory calibrated
to produce 4 mA at zero scale reading and 20 mA at full scale reading.
The following procedure should be used if the pressure versus output
signal relationship needs to be checked.
1. With unit connected to the companion receiver per preceding
instructions, insert an accurate milliammeter with a full scale read-
ing of approximately 30 mA in series with the current loop.
2. Vent both pressure ports to atmosphere and, if necessary, adjust
pointer zero screw to align pointer with zero on scale.
A controllable pressure source capable of reaching the full scale
range should be connected to either high pressure port. Plug the
other high pressure port and vent one or both low pressure ports to
atmosphere. The instrument must be ranged in the same position
in which it will be used. Standard factory calibration and ranging is
done with unit vertical.
3. Apply electrical power to the system and check for proper operation
by slowly increasing pressure and observing whether the loop cur-
rent increases above the 4 mA zero pressure reading.
4. A spanner type key is supplied to adjust span and zero. This helps
to reduce unauthorized tampering. Apply pressure until pointer
aligns with full scale reading and adjust the SPAN knob for a 20 mA
reading.
5. Relieve all pressure, allow a few seconds for setting and adjust the
ZERO knob for a 4 mA current loop reading.
6. The SPAN and ZERO controls are slightly interactive so steps 4 &
5 should be repeated a few times until readings of 4 and 20 mA are
obtained consistently.
7. Remove the milliammeter from the current loop and proceed with
final installation of the transmitter and receiver.
Figure A
Figure B
Figure C
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