LA1 and LA2 - Load-Cell Conditioner Upper Board

LOAD-CELL CONDITIONER UPPER BOARD
LA1 (Ultra-Low Tempco) LA2 (Low Tempco)

FEATURES

Differential preamplifier with gains from 20 to 800

Floating 5, 10, 15 Vdc excitation supply

Up to 115 mA at 10 Vdc to drive four 350 ohm bridges in parallel

Ratiometric operation with remote excitation sense

4 or 6-wire bridge connection

Front-panel accessible fine span and finebridge balance adjustments

Calibration push-button

2-Hz low-pass active filter for additional 50 dB NMR at 50/60 Hz

Deadload offset to ±60% of input

Low tempco: ±10 ppm/°C (LA1), ±30 ppm/°C (LA2)

APPLICABLE INSTRUMENTS

204B (3 3/4 digits)

2003B (4 1/2 digits)

2004 (4 3/4 digits)

The LA1 and LA2 are upper-board options which convert Models 204B, 2003B and 2004 DC voltmeters into strain gauge/microvoltmeters. They are designed for use with pres-sure transducers, load cells and other bridge transducers which require excitation and preamplification of microvolt signals.
Option LA1 uses wirewound resistors, which provide an ultra-low tempco of ±0.001%/°C (±10 ppm/°C). It is recom-mended for use with Model 2004, a high-accuracy 4 3/4 digit voltmeter.
Option LA2 uses metal-film resistors, which provide a tempco of ±0.003%/°C (±30 ppm/°C). It is recommended for use with Models 204B and 2003B.

PREAMPLIFIER AND EXCITATION SUPPLY
The LA1 and LA2 are used in conjuction with the "-3" and "HZ" DC input configurations of the host meters. It adds a true-differential preamplifier, which can be configured for gains from 20 to 800, plus a floating constant-voltage excitation supply, which can be configured for 5, 10 or 15 V dc. The supply can provide 115 mA at 10 V dc, so that one LA board can excite up to four 350l bridges in parallel. The reference used in the A/D converter of the host meters is derived from excitation-voltage sense lines for true ratiometric operation.

SPECIFICATIONS

PREAMPLIFIER
Input configuration: Differential, ratiometric
Gain range: 20 to 800
Preamplifier output swing: 0.5 V to +4.0 V
Coarse-span adjustment: 125 overlapping ranges with fine adjustment
Fine-span adjustment: Front-panel potentiometer
Coarse-bridge balance adjustment: ±60% of bridge output with external resistor
Fine-bridge balance adjustment: Front-panel potentiometer
Active filter: 2.1 Hz corner frequency with 40 dB/decade roll-off

NOISE REJECTION
NMR, 50/60 Hz: 50 dB (to be added to NMR of host DPM)
CMR, SIG LO to SIG GND: 80 dB, DC to 60 Hz
CMV, SIG LO to SIG GND: ±1 V, DC to 60 Hz
CMR, SIG GND to PWR GND: 120 dB, DC to 60 Hz
CMV, SIG GND to PWR GND: 1500 Vp per HV test, 354 Vp per IEC spacing

ACCURACY AT 25 °C
Zero tempco referred to input (RTI), typ: ±0.3 µV/°C
Zero tempco referred to output (RTO), typ: ±0.6 µV/°C
Span tempco, LA1: ±0.001%/°C(±10 ppm/°C)
Span tempco, LA2: ±0.003%/°C (±30 ppm/°C)

Operation of LA upper board with DPM main board. The excitation supply is referenced to ground through the external bridge and the ratiometric reference circuit, thereby providing high immunity to power-line and load variations.

EXCITATION SUPPLY
Configuration: Constant-voltage
Voltage sense: Internal or remote
Bridge connection: 4 or 6-wire
Voltage settings: 5, 10, 15 V dc, (jumper-selectable)
Load current, max: 125 mA at 5 V, 115 mA at 10 V, 67 mA at 15 V

POWER
AC input voltage: 120/240 V ac +10%/15%
AC frequency: 50/60 Hz
Power consumption at max excitation load: 0.5 W

ENVIRONMENTAL
Operating temperature: 0 to 50°C
Storage temperature: -40 to +85°C
Relative humidity: 95% at 40°C(non-condensing)

MECHANICAL
Form factor: Newport DIN 1A upper board
Dimensions: 3.35 x 4.69 in (85 x 119 mm)
Connector: 36-pin, double-row, solder-type