ETC 945

Models 940 and 945 DC Transmitters
Features
Description
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4 to 20mA Output
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0 to +10V Input - Model 940
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0 to 50 mV Input - Model 945
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700 Volts DC Isolation
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PC Board Mount Modular Design for
OEM Applications
The CALEX Model 940 and 945 are fully DC isolated voltage
to current transmitters. They are ideal for eliminating ground
loops and common mode problems in data acquisition and
process control systems. The 20 Volt maximum output
compliance voltage allows a loop resistance of up to 1000
ohms. The isolation input to output is 700 Volts DC. The input
and output are also isolated from the unregulated +14 to +16
VDC power source.
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Convenient Mounting Kit Available for
End User Applications
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Powered by 14 to 16 Volts
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24 VDC Operation Available
Model 940 and 945 Block Diagram
2401 Stanwell Drive
Concord, CA 94520-4841
(510) 687-4411 • Fax (510) 687-3333
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CALEX FaxFACTS: 319
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A
Models 940 and 945 DC Transmitters
Specifications
Input
Voltage
Resistance
Operation
940
945
0 to +10 Volts
0 to 50 mV
10 megohm minimum
Output
Current
4 to 20 mA
Load Resistance
For 4 to 20 mA operation, a 200 ohm external cermet
potentiometer is required to set 4 mA Zero Current. Connect
the wiper to pins 6 and 8. Connect one end terminal to pin 7
with a 604 ohm 1% resistor in series. Connect the other end
terminal to pin 8. Tie pin 4 to pin 3. Reference Model 940 Block
Diagram.
0 to 1000 ohm
Compliance
20 Volts maximum
Frequency Response
Rise Time
0.9 ms
Settling Time to 0.1%
Noise
2.5 ms
1 mA P-P
50 mA P-P
1 kHz bw
20 MHz bw
Power Supply Sensitivity
Zero
S pan
Accuracy @ 25°C
5 mA/ Volt
0.005%/Volt
0.1% of Full Scale
Linearity
0.05% of Full Scale
Temperature Coefficient
Zero
S pan
Isolation - Input to Output
Mechanical Specifications
400 Hz @ 3 dB
0 to 55°C
0.0035%/°C of Full Scale
0.0035%/°C of Full Scale
700 Volts DC
or Power Supply
25 pF
Capacitance
Pow er Requirements
DC Voltage
Current
14 to 16 Volts DC
125 mA
Zero Set
BOTTOM VIEW
External Cermet Potentiometer Required to set 4mA Zero current.
External Pot may be used to set output current 0 to 20mA.
Environment
P a cka g e
Size (inches)
2" x 2" x 0.6"
2.5 oz.
1
2
3
4
5
6
7
8
9
10
+INPUT
-INPUT
RETURN
RETURN
CURRENT OUTPUT
Reference Model 940/945 Block Diagram
Reference Model 940/945 Block Diagram
Reference Model 940/945 Block Diagram
-DC POWER
+DC POWER
A
2401 Stanwell Drive
Concord, CA 94520-4841
(510) 687-4411 • Fax (510) 687-3333
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CALEX FaxFACTS: 319
1997
Weight
Pin Assignments
Encapsulated Plastic Module
Models 940 and 945 DC Transmitters
Mounting Kit
The MK940 mounting kit is an optional printed circuit board
that provides the necessary potentiometers and a connector
for a complete turnkey system.
The 940/MK940, when ordered as a combination, is shipped
from the factory configured as a 0 to +10 Volt input, 4 to 20mA
output, isolated transmitter. The 945/MK940, when ordered
as a combination, is shipped from the factory configured as
a 0 to 50 mV input, 4 to 20 mA output, isolated transmitter.
Note in the schematic, Figure 1, that C1, R1, R2, R3, and R5
are included on the board. The other designated components
are user supplied for other applications. Also note that R8
through R11 are not connected to the rest of the circuit. For
24 VDC operation, add a “-24” to the MK940, i.e. 945/MK94024
Figure 2 shows the outline of the MK940 card and the lettered
pin assignments. The card includes a Model 015 connector
with edge guides and has eyelets for soldering wires. The
components described as jumpers are wire connections
although they have a ceramic body the size of a ¼W resistor.
NOTE:
C1, R1, R2, R3, R5 ARE INCLUDED.
ALL OTHER COMPONENTS ARE USER
SUPPLIED FOR SPECIFIC APPLICATIONS.
FIGURE 1. MK940 Schematic
A
FIGURE 2. MK940 Card
2401 Stanwell Drive
Concord, CA 94520-4841
(510) 687-4411 • Fax (510) 687-3333
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CALEX FaxFACTS: 319
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Model 940/945
Models 940 and 945 DC Transmitters
Applications
The 940/MK940 may be configured for 4 to 20mA output, as
a constant current source, as a 0 to 1mA current source, 0
to 5V output, voltage input and 1 to 5V output, or an isolated
voltage input and 4 to 20V output with a single pole 10Hz input
filter. Figures 3 through 8 illustrate these configurations with
the Model 940/945 and MK940 mounting kit. The R-numbers
refer to locations labeled on the MK940. All fixed value
resistors should be metal film 1% type. Where a potentiometer
is shown, use a multiturn trim pot with a CERMET resistance
element. The hole pattern is for industry standard
potentiometers such as Bourns “3006Y”, Spectrol “43”, and
Beckman “89” series.
MK940 Application
Isolated 0 to 20mA Output
NOTE:
R6 IS A 1% METAL FILM 1/4 W
RESISTOR.
ZERO CURRENT MAY BE 100µA
FIGURE 3.
Shows an isolated 0 to 20mA current loop. In this application the ZERO pot is not used and is replaced by a wire jumper. R6 parallels an internal
50 ohm resistor to change the scale factor. The zero current may be from 10nA to 100µA. Zero current must be checked with a short between pins
F and H, or 0 Volts input. Do not leave the input open.
MK940 Application
Isolated Constant Current Source
FIGURE 4.
Is a potentiometer adjust 0 to 20mA constant current source which is isolated from the power supply. The jumper in place of R4 ensures that the
input is zero volts. Do not apply any control voltage to the input. The output will drive zero to 1000 ohms with a 15 volt power supply.
2401 Stanwell Drive
Concord, CA 94520-4841
(510) 687-4411 • Fax (510) 687-3333
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CALEX FaxFACTS: 319
1997
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Models 940 and 945 DC Transmitters
MK940 Application
Isolated 0 to 1mA Current Source
NOTE:
R5 IS A 1% METAL FILM 1/4 W
RESISTOR.
FIGURE 5.
Zero to 1mA current source. The load resistance may be 0 to 20,000 ohms. Other values of full scale current may be set by changing R5. The maximum
output current is determined by 0.8V/(R5+50) and is limited to 20 mA.
MK940 Application
Isolated 0 to 5 Volts Out
A
R6 IS A 1% METAL FILM 1/4 W
RESISTOR.
FIGURE 6.
Shows a voltage to voltage transmitter. Note that this configuration will have a 249 ohm output source resistance which will produce an error of 2.5%
if driving a 10,000 ohm load or 0.25% if driving a 100,000 ohm load. R6 parallels the internal 50 ohms to produce 20mA output with full scale input.
There will be 0.8 Volts between pins 7 and 4 with full scale input.
2401 Stanwell Drive
Concord, CA 94520-4841
(510) 687-4411 • Fax (510) 687-3333
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CALEX FaxFACTS: 319
1997
NOTE:
Models 940 and 945 DC Transmitters
MK940 Application
Isolated Voltage In - 1 to 5 Volts Out
NOTE:
R13 IS A 1% METAL FILM 1/4 W
RESISTOR.
FIGURE 7.
Is similar to Figure 6 except R1 and R2 are used to set 4mA, or 1 Volt at the output with zero Volts input. Also R5 is zero ohms.
MK940 Application
Isolated Voltage In - 4 to 20 Volts Out
with Single Pole 10Hz Input Filter
A
1997
R13 IS A 1% METAL FILM 1 W
RESISTOR.
FREQUENCY LIMIT - INPUT FILTER
DC TO 10 Hz BAND PASS
FIGURE 8.
Shows how to add a low pass filter at the input where the 400Hz bandpass may be too high and is causing noise problems. C4 should be a low dielectric
absorption capacitor such as a X7R ceramic or a film capacitor. As discussed in Figure 6, R13 is the output source resistance and in this case would
produce a 10% error when driving a 10,000 ohm load, and a 0.01% error when loaded by a 10 Megohm input digital voltmeter.
2401 Stanwell Drive
Concord, CA 94520-4841
(510) 687-4411 • Fax (510) 687-3333
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CALEX FaxFACTS: 319
NOTE: