The Micro Series load cell and microvoltmeter is a high-sensitivity monitor and controller for use with load cells, strain gauges and microvolt input signals where high accuracy and stability are required.
Usage as a DC microvoltmeter provides sensitivity down to 20 mV full scale with 1 ĩV resolution. With a digital multiplier of five, 99,999 counts can be displayed with a sensitivity of 0.2 ĩV per count. A moving average filter with a time constant of 1.2 sec or greater should then be selected.
Usage as a load cell meter allows six-wire hookup and scaling for direct readout in engineering units, such as pounds, kilograms or PSI. Scaling can be via front panel pushbuttons or a computer. Zero may be set from -99,999 to +99,999. Range may be scaled from 0 to ą99,999. Digital scaling and calibration eliminate drift caused by potentiometers in non-microcomputer based meters.
An isolated 10 Vdc excitation supply can provide up to 120 mA of current to power up to four 350-ohm load cells in parallel. The meter operates in a ratiometric mode to eliminate errors due to supply variations. When excitation sense inputs are used in 6-wire connection, the meter compensates for variation in resistance of the transducer leads, thereby allowing long cable runs.
Fast Read Rate plus Peak Capture
Micro Series meters use Concurrent Slope (Pat 5,262,780) analog-to-digital conversion, which allows up to 60 conversions per second, while integrating the signal over a full power cycle. High read rate is ideal for peak value capture and for real-time computer interface and control. Peak capture is standard.
Selectable Signal Filtering
The displayed readings and the data outputs can be separately selected to be either unfiltered or filtered.
An unfiltered selection updates after each conversion for fastest response, up to 60/sec, while integrating the input signal over a full power cycle. Fast read rate provides true peak readings and aids in control applications.
A batch average filter selection averages each 16 conversions for an update every 1/4 sec.
An adaptive moving average filter selection provides a choice of 8 time constants from 80 ms to 9.6 s. When a significant change in signal level occurs, the filter adapts by briefly switching to the shortest time to follow the change, then reverts back to its selected time constant. Another choice is Auto, which provides an automatic time constant selection based on the signal noise characteristics.
Micro Series DC, process and load cell meters allow easy setting of scale and offset by either of two methods.
With the coordinate reading method, the meter reads the high and low signal values, and the user enters the desired high an low reading values. The meter then calculates the span multiplier and offset. This method is ideal if an external calibration reference is available.
With the manual coordinate method, the user enters the high and low input values in Volts plus the desired high and low reading values. This method is suitable if an no external calibration reference is available.
For weighing applications, auto-tare is standard. Auto-tare can set the displayed value to zero to subtract the weight of an empty container. Auto-tare may be controlled by an external pushbutton contact closure or logic signal through an input on the power supply connector. The tare value is stored in memory. Additional capabilities for weighing applications are provided by the Micro weight / scale meter, as described in a separate web page.
Other Features and Options
Plug-in isolated analog output, dual-setpoint controller, and RS232/485 serial communications boards can upgrade Micro an Mighty Series load cell meters from stand-alone monitor to system interface and control. With the optional analog output board, the meter can serve as a 0-10 V or 4-20 mA transmitter.
Micro Series instruments can be powered from 95-240 Vac ą10% and 95-370 Vdc, or optionally from 12-34 Vac and 10-48 Vdc. Any setup functions and front panel keys may be locked out for simplified usage and security. The popular 1/8 DIN version with 0.56″ high digits is environmentally sealed to NEMA-4X (IP65) from the front when panel mounted, and is available with red or green LEDs.
DC Microvoltmeter Inputs
Error at 25°C
Load Cell Inputs
Error at 25°C
DC Microvolts & Load Cell
0.0015% of reading/°C
CMR, DC to 60 Hz
NMR at 50/60 Hz
90 dB with min filtering
Concurrent Slope™ (Pat 5,262,780)
60/s at 60 Hz, 50/s at 50 Hz
56/s at 60 Hz, 47/s at 50 Hz
3.5/s at 60 Hz, 3/s at 50 Hz
5 digits, 7-segment
Available with 0.56", 1.0", 4.0" or 5.0" digits.
High brightness red. Green available with 0.56" digits.
-99999 to +99999 or -99990 to +99990
(count by 10 with rounding)
Minus sign, 2 red LED lamps
95-240 Vac ą10% and 95-370 Vdc
12-34 Vac and 10-48 Vdc
DC or 49-440 Hz
Safety-rated to 250 Vac, meter ground to earth ground,
DC to 60 Hz, 4.2 kVp per High Voltage Test
5 Vdc ą5%, 100 mA max
10 Vdc ą5%, 120 mA max
24 Vdc ą5%, 50 mA max
50 Vdc to meter ground
0°C to 60°C
-40°C to 85°C
95% at 40°C, non-condensing
NEMA-4X (IP-65) when panel mounted
Load Cell Meter Connections
In 4-wire connection, the excitation and sense lines are tied together. The meter can make ratiometric corrections for supply voltage variations, but not compensate for variations in lead resistance. This connection is often used with short cable runs.
In 6-wire connection, the sense lines are separate from the excitation lines, thereby eliminating effects due to variations in lead resistance. This allows long cable runs in outdoor environments with temperature extremes.
For large scales, up to four 350 ohm load cells can be powered by a single Micro load cell meter, whose excitation output is rated 120 mA at 10 V. The excitation and sense points of the four bridges are connected in parallel through a summing box.
Sample Load Cell Meter Applications
To read the net weight of an object, the empty container is first weighed, and an external button is pushed to zero out the display. The meter will then read net weight when an object is added to the empty container. The tare value is stored in memory for subsequent readings.
Determining Volume Using Load Cells
An easy way to determine volume of an irregularly shaped tank with no need for linearizing is to weigh the tank using load cells. The meter will automatic- ally tare out the weight of the empty tank and then scale the load cell signals to units of volume, such as gallons.
Peak Capture for Testing the Tensile Strength of Wire
Peak readings are automatically captured at rates up to 60 per second, while the display updates at a legible 3.5 per second. The peak reading can be recalled at the push of a button or be always displayed. It can also be transmitted to a computer via RS232 or RS485.