Datel DMS-20LCD-4/20 Series Manual - Halaman 3

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3 ½ D I G I T , L C D D I S P L A Y , 4 - 2 0 m A L O O P - P O W E R E D M E T E R S

DMS–20LCD–4/20B (Bipolar Reading Model)

The DMS-20LCD-4/20B's zero-offset circuit differs from the unipolar 'S'

model described above in that with the 'B' model, a half-scale 12mA input is

normally set to display "000". Therefore, all of the of the DIP-switch settings

in Table 2 assume a reading of "000" is desired with a 12mA input. Display

readings other than those shown in Table 2 are possible, contact DATEL for

more information.

When configuring the DMS-20LCD-4/20B for the first time, or when selecting

a new range, set both R3 and R7 fully clockwise (roughly 22 turns) to their

minimum offset/minimum-span positions, respectively. Then select the

desired readings from Table 2 and configure DIP-switches SW1, SW2, and

SW3 accordingly.

The procedure below illustrates how to calibrate the DMS-20LCD-4/20B to

its factory-calibrated readings of "–1000" with a 4mA input and "1000" with a

20mA input. When performing DIP-switch settings, be sure the DIP-switch's

small actuators are firmly engaged in their fully-ON or fully-OFF positions.

1. Set both R3 and R7 fully clockwise.

2. Select DIP-switch setting #1 from Table 2.

3. Apply a precision 12mA input and adjust R3 until the meter's display

reads "000".

4. Apply a precision 20mA input and adjust R7 until the meter's display

reads "1000".

5. Apply a precision 4mA input and the display should read "–1000".

Repeat steps 3 and 4 to make sure the two adjustments did not

affect one another.

Table 2. DMS-20LCD-4/20B (Bipolar Model)

DIP-Switch Settings

Display Reading

4mA

12mA

20mA

1. –600 to –1000

000

600 to 1000

2. –350 to –650

000

350 to 650

3. –250 to –400

000

250 to 400

4. –150 to –250

000

150 to 250

5. –100 to –150

000

100 to 150

Examples

(DMS-20LCD-4/20B-Bipolar Model)

1. Desired display readings are:

4mA = "–1.00"

20mA = "1.00"

Use DIP-switch setting #5 in Table 2 and enable decimal point DP2 via

SW5. Apply 12mA and adjust R3 so the display reads "0.00". Apply

20mA and adjust R7 so the display reads "1.00". Apply 4mA and verify

that the display reads "–1.00", readjust R3 and R7 if necessary.

DATEL, Inc., Mansfield, MA 02048 (USA) • Tel: (508)339-3000, (800)233-2765 Fax: (508)339-6356 • E–mail: [email protected] • Internet: www.datel.com

SW1

SW2

SW3

Off

2. Desired display readings are:

4mA = "–450"

20mA = "450"

Use DIP-switch setting #2 in Table 2. Apply 12mA and adjust R3 so the

display reads "000". Apply 20mA and adjust R7 so the display reads

"450". Apply 4mA and verify that the display reads "–450". Repeat

adjustment procedure if necessary. For these display readings, no

decimal points are used. Set SW4, SW5 and SW6 to OFF.

3. Desired display readings are:

4mA = "–650"

20mA = "650"

Notice that these readings can be obtained using either DIP-switch

setting #1 or DIP-switch setting #2 in Table 2. In situations like this where

DIP-switch settings overlap, less-sensitive R3/R7 adjustments can be

achieved if the higher DIP-setting # is selected (setting #2 in this example).

Apply 12mA and adjust R3 so the display reads "000". Apply 20mA and adjust

R7 so the display reads "650". Apply 4mA and verify that the display reads "–

650". Repeat adjustment procedure if necessary.

DMS-20LCD-4/20P (Positive Reading Model)

The DMS-20LCD-4/20P's Zero-Offset circuit is optimized to produce

positive readings at both 4mA and 20mA input levels. As shown in Table 3's

first three columns, a 4mA input can be typically adjusted (using R3, Zero/

Offset Adjust) to display any positive reading between "000" and "800". The

corresponding 20mA-input reading is then added to the 4mA offset as a

differential whose magnitude is varied by adjusting R7 (Gain/Span Adjust).

The 'Differential Range' column in Table 3 lists the nominal differential

display-readings which can be obtained with R7 at, or very close to, its full-

clockwise, minimum span position. The Differential Range column can be

used as a guide when configuring the meter for the majority of user

applications. Higher differential ranges are obtainable; however, the use of

higher differential readings results in correspondingly-lower positive

readings with 4mA inputs, that is, R3's clockwise adjustment-range is

reduced. Example #3 below illustrates this concept. Please contact DATEL if

there is any doubt as to whether or not the DMS-20LCD-4/20P can be

configured for your display readings requirements.

The first step when configuring the DMS-20LCD-4/20P for the first time, or

when selecting a new range, is to set R3 fully counterclockwise and R7 fully

clockwise (roughly 22 turns) to their minimum offset/minimum span

positions, respectively.

The next step is to calculate the required display differential-reading; this is

accomplished by subtracting the desired 4mA display reading from the

desired 20mA display reading, disregarding decimal points. Then, using the

calculated differential display-reading to select the appropriate DIP-switch

setting # from Table 3, configure DIP-switches SW1, SW2, and SW3

accordingly. Make certain that the DIP-switch's small actuators are firmly

engaged in their fully-ON or fully-OFF positions.

The procedure below describes how to calibrate the meter for an applica-

tion which the DMS-20LCD-4/20P easily accommodates: displaying the

output of a 4-20mA transmitter, that is, "04.0" with a 4mA input and "20.0"

with a 20mA input.

DMS-20LCD-4/20