Model945 - Calex Mfg. Co. Inc. - Datasheet.Directory

Models 940 and 945 DC Transmitters

Manufacturing Company, Inc.

• Concord, California 94520 • Ph: 925/687-4411 or 800/542-3355 • Fax: 925/687-3333 • www.calex.com • Email: sales@calex.com

Features

!4 to 20mA Output

!0 to +10V Input - Model 940

!0 to 50 mV Input - Model 945

!700 Volts DC Isolation

!PC Board Mount Modular Design for

OEM Applications

!Convenient Mounting Kit Available for

End User Applications

!Powered by 14 to 16 Volts

!24 VDC Operation Available

Description

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.

Model 940 and 945 Block Diagram

Models 940 and 945 DC Transmitters

Manufacturing Company, Inc.

• Concord, California 94520 • Ph: 925/687-4411 or 800/542-3355 • Fax: 925/687-3333 • www.calex.com • Email: sales@calex.com

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Specifications Operation

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.

Mechanical Specifications

BOTTOM VIEW

Models 940 and 945 DC Transmitters

Manufacturing Company, Inc.

• Concord, California 94520 • Ph: 925/687-4411 or 800/542-3355 • Fax: 925/687-3333 • www.calex.com • Email: sales@calex.com

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/MK940-24

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.

FIGURE 2. MK940 Card

FIGURE 1. MK940 Schematic

NOTE: C1, R1, R2, R3, R5 ARE INCLUDED.

ALL OTHER COMPONENTS ARE USER

SUPPLIED FOR SPECIFIC APPLICATIONS.

Model 940/945

Models 940 and 945 DC Transmitters

Manufacturing Company, Inc.

• Concord, California 94520 • Ph: 925/687-4411 or 800/542-3355 • Fax: 925/687-3333 • www.calex.com • Email: sales@calex.com

MK940 Application

Isolated 0 to 20mA Output

NOTE: R6 IS A 1% METAL FILM 1/4 W

RESISTOR.

ZERO CURRENT MAY BE 100µA

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.

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

MK940 Application

Isolated Constant Current Source

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.

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.

Models 940 and 945 DC Transmitters

Manufacturing Company, Inc.

• Concord, California 94520 • Ph: 925/687-4411 or 800/542-3355 • Fax: 925/687-3333 • www.calex.com • Email: sales@calex.com

NOTE: R5 IS A 1% METAL FILM 1/4 W

RESISTOR.

NOTE: R6 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.

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.

MK940 Application

Isolated 0 to 1mA Current Source

MK940 Application

Isolated 0 to 5 Volts Out

Models 940 and 945 DC Transmitters

Manufacturing Company, Inc.

• Concord, California 94520 • Ph: 925/687-4411 or 800/542-3355 • Fax: 925/687-3333 • www.calex.com • Email: sales@calex.com

MK940 Application

Isolated Voltage In - 1 to 5 Volts Out

MK940 Application

Isolated Voltage In - 4 to 20 Volts Out

with Single Pole 10Hz Input Filter

NOTE: R13 IS A 1% METAL FILM 1/4 W

RESISTOR.

NOTE: R13 IS A 1% METAL FILM 1 W

RESISTOR.

FREQUENCY LIMIT - INPUT FILTER

DC TO 10 Hz BAND PASS

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.

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.