Dwyer MS User Manual
Page 2
Electrical Connection:
2-Wire Operation, continued:
The connections to the transmitter are made through a two circuit
European style terminal block CONN6 located at the bottom of the main
PCB board. Polarity is indicated by + and – signs on the PCB board. Do
not connect to the (V) terminal.
Figure 1
An external power supply delivering 10 to 35 VDC with a minimum
current capability of 40 milliamps must be used to power the control loop
in which the Magnesense
®
transmitter is connected. Refer to Fig. 1 for
connection of the power supply, transmitter and receiver. The range of
appropriate receiver load resistances (R
L
) for the power supply voltage
available is given by the formula and graph in Fig. 2. 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.
Figure 2
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.
3-Wire Operation:
The connections to the transmitter are made through a three circuit
European style terminal block. Connect the power and signal leads to the
corresponding terminals as shown in Fig. 3. When using a DC supply,
the positive of the supply should be connected to (+) and the negative
connected to (-). Connecting the leads in reverse will not damage the
device but it will not operate. The DC supply should be capable of
providing 20 mA or more of current per Magnesense
®
transmitter.
When using an isolated AC supply, either leads of the supply may be
connected to (-) and (+). The input diode of the device half wave rectifies
and filters the applied AC voltage. A small DC current of less than 20 mA
is thus drawn through the transformer. The transformer used for the AC
supply must be capable of handling this small DC current. Use a UL 1584
Class 2 rated transformer rated between 24 V and 30 VAC, 40 VA or
larger, 50/60 Hz. UL 1584 Class 2 rated transformers are limited to 30
VAC maximum under any conditions at nominal line. The AC input
voltage to the device is thus limited to a minimum of 21.6 at low line (24
V-10%) and 33 V at high line (30 V+10%).
Figure 3
The output of (V) is 0 to 5 VDC or 10 VDC depending on model. As much
as 10 mA may be drawn from (V) without affecting accuracy. This limits
the minimum load RL connected to Vo to 1 KΩ or higher. Remember to
keep the wiring resistance between the output and the receiver R
L
low
compared to value of R
L
. While the voltage at the terminals remains
unchanged with a 10 mA current flow, resistive losses in the wiring do
cause errors in the voltage delivered to R
L
. For a 1% accurate gauge, a
good rule of thumb would be to keep the resist 0.1% of the value of R
L
.
This will keep the error caused by current flow below 0.1%.
To minimize noise in the signal use shielded cable. The common line
may also be grounded.
Pressure Connections
Two integral tubing connectors are provided. They are designed to fit
3/16˝ (5 mm) ID tubing. Connect the high pressure to the High side as
shown in Fig. 4. Be sure the pressure ratings of the tubing exceed that
of the operating ranges.
Figure 4
V
–
+
+
–
RL
P.S.
POWER SUPPLY VOLTAGE
0
5
10 13
15
20
25
30
35
40
MAXIMUM VALUE (1250
Ω )
OPERATING
REGION
TOT
AL RECEIVER RE
S
IS
TANCE (
Ω
)
R
L
MAX =
V
ps
- 10.0
20mA DC
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
50
HIGH
LOW
POWER SUPPLY
17 TO 36 VDC
OR
21.6 TO 33 VAC
RECEIVER
CONN6
+
V
Ø
R
L
DO NOT EXCEED SPECIFIED SUPPLY
VOLTAGE RATINGS. PERMANENT DAMAGE
NOT COVERED BY WARRANTY WILL RESULT.
CAUTION
A-26P:Magnesense bulletin 2/21/11 12:13 PM Page 2