Model 202A-S - Low-Cost, 3 1/2 Digit Strain/Microvoltmeter

LOW-COST, 3 1/2 DIGIT STRAIN / MICROVOLTMETER
MODEL 202A-S

1/8 DIN (2A) Case

Connections Diagram

STANDARD FEATURES
Programmable preamplifier
Isolated 10-24 Vdc bridge excitation supply
Independent bridge-balance, zero & span adjustments
±1,999-count display span
120 dB CMR, 70 dB NMR
Bright, 14.2 mm (0.56 in) LED display
Automatic zero and polarity
Display hold and test
115/230 Vac power
EMI/RFI filter for AC power
Screw-terminal barrier strip
Short (4.1 in, 104 mm deep) 1/8 DIN case

OPTIONS
Isolated 9-32 Vdc power
Isolated 26-56 Vdc power
NEMA-4 splash-proof lens cover

Model 202A-S is a low-cost 3 1/2 digit panel meter in a short 4.1 in (104 mm deep) 1/8 DIN case for applications that require bridge excitation and resolution down to 10 microvolts. Zero, span and bridge-balance adjustments are accessible behind the lens, so that the 202A-S can read out directly in engineering units for a wide range of bridge inputs or other low-level signals.

APPLICATIONS
Model 202A-S is primarily intended as a digital indicator for pressure cells and metal-foil load cells. It can also be used as a low-level, high-impedance process meter with zero and span adjustments, or as a DC voltmeter with resolution down to 10 microvolts, required by 50 mV current shunts.

RESOLUTION AND ACCURACY
Resolution is 1 part in ±1,999 counts, or 0.05% of full scale. Accuracy is 99.9%. A ratiometric reference input eliminates AC line and load regulation errors and reduces overall meter span tempco to 0.01% of reading/°C.

BRIDGE EXCITATION SUPPLY
The built-in excitation supply of the 202A-S is transformer-isolated to 500 Vac from the rest of the meter. A multiturn potentiometer accessible behind the lens allows adjustment of the output voltage from 10 to 24 Vdc. Maximum output current is 30 mA.

MICROVOLT PREAMPLIFIER
The preamplifier of the 202A-S provides an input impedance in excess of 1 G to ensure that the signal source is not overloaded. Gains of 1, 10 and 100 are selectable by solder bridges and provide resolutions of 1000, 100, and 10 µV/count, respectively. Typical offset drift is only 0.3 µV/°C.

OPTIONS
Mechanical options are a PCB edge connector for hand-shake signals and a splash-proof lens cover which meets NEMA-4 requirements. Power options are isolated 9-32 Vdc and 26-56 Vdc.

SPECIFICATIONS

ANALOG INPUT	Most-sensitive scaling	Least-sensitive scaling
Range	±19.99 Mv	2.5 V (limited by CMV)
Resolution	10 µV/count	1 mV/count
Preamplifier gain	100	1
Gain attenuator	1	0.001

Configuration: Differential, ratiometric
Polarity: Bipolar
Input resistance: 1 G
Bias current: 1 nA typ, 5.5 nA max
Maximum voltage: 50 V
Coarse preamplifier gains: 1, 10, 100
Gain attenuator: Adjustable from 0.001 to 1
Bridge-balance range: ±50% of bridge span
Zero-adjustment range: -1,000 to +1,000 counts
Span-adjustment range: 0 to 2,000 counts

NOISE REJECTION
NMR, SIG HI to SIG LO: 70 dB, 50/60 Hz
CMR, SIG GND to SIG HI: 120 dB at gain 100, DC to 60 Hz
CMV, SIG GND to SIG HI or LO: +2.5 Vdc
CMR, SIG GND to PWR GND: 120 dB, DC to 60 Hz
CMV, SIG GND to PWR GND: 1500 Vp test, 354 Vp per IEC spacing

ACCURACY AT 25°C
Error, max: ±0.05% of reading ±1 count
Balance tempco: ±0.3 µV/°C typ, ±1.0 µV/°C max
Zero tempco: ±0.01% of zero/°C
Span tempco, ratiometric: ±0.03% of reading/°C
Span tempco, non-ratiometric: ±0.3 µV/°C
Full-scale step response: 1.0 s
Warmup to rated accuracy: 10 min

ANALOG-TO-DIGITAL CONVERSION
Technique: Dual-slope, average-value
Signal integration period: 100 ms
Read rate: 2.5/s

BRIDGE EXCITATION SUPPLY
Output voltage: Adjustable 10 to 24 Vdc
Output current: 30 mA at 10 Vdc decreasing to 12 mA at 24 Vdc
Line regulation: ±0.01%/V of AC power
Load regulation: ±0.5%
Ripple at 50/60 Hz: ±0.01%
Tempco: ±0.02%/°C
Reference signal: 1.0 V typ at 10 V output (Eliminates line and load regulation errors and reduces overall meter span tempco to ±0.01%/°C)

DISPLAY
Display Type: 7-segment, red LED
Display Height: 0.56 in (14.2 mm)
Symbols: 1.8.8.8
Decimal points: Three positions, programmable by jumpers behind lens or at connector, 10 mA sink
Overrange indication: Three least-significant digits blanked

DIGITAL INPUTS
Level: TTL or 5 V CMOS compatible

POWER
AC voltages: 115 or 230 Vac ±15%
AC frequency: 49-440 Hz
DC voltages: 9-32 Vdc, isolated to 300 Vp; 26-56 Vdc, isolated to 300 Vp
Power consumption: 3.7 W max
Output Voltages: +4.7 Vdc and 4.7 Vdc ±5%, 10 mA max

ENVIRONMENTAL
Operating temperature: 0 to 60°C
Storage temperature: 40 to +85°C
Relative humidity: 95% at 40°C (non-condensing)

MECHANICAL
Dimensions: Newport DIN1A (1/8 DIN) case (see Mechanical section for drawings)
Weight: 15 oz (425 g)
Case material: 94V-0 UL-rated polycarbonate
Connector for signal and power: D4 screw-terminal barrier strip (standard)
Connector for control lines: D1 36-pin PCB edge connector (optional)