Micro Series weight meters are available with digit heights from 0.56″ (14.2 mm) to 5.0″ (127 mm) for incorporation in an indoor scale or reading across an outdoor yard. The meters can utilize two signal conditioner boards: the Micro load cell signal conditioner board, which provides full-scale ranges of 20, 50, 100, 250 and 500 mV with 4- or 6-wire load cell hookup, and the Micro DC signal conditioner board, which allows the meter to accept preconditioned signals such as 0-10 V or 4-20 mA. Options include setpoint control, analog output and digital communication boards.
Display & Setpoint Functions
Setpoint Offset. The ON/OFF setpoint control action can be programmed to occur with a specified offset. For instance, if bags are to be filled to 100 lbs and the material delivery spout is known to hold and dispense an additional 2.5 lbs following shut-off, an offset of -2.5 lbs can be programmed. The setpoint can then be set to 100 lbs, and the filling valve will be automatically shut off when the measured weight reaches 97.5 lbs.
Count-by Function. The weight meter can be programmed so that the display is rounded off to multiples of 1, 2, 5, 10, 20, 50 or 100. For example, if count-by 10 is selected, the meter will display 20 for an internal count of 15 to 24.
Fixed Zero. The display can be shifted left to allow a fixed zero to be displayed to the right. This allows values up to 999,990 to be displayed.
Auto-zero Function. An auto-zero limit from 0 to 9 counts can be programmed to compensate for load cell drift. Whenever the meter comes to rest within that limit from zero, it will auto-zero. Entering 0 disables auto-zero.
Two Tare Functions. The weight meter offers two types of tare: auto-tare and manual tare. In auto-tare, an input line is grounded by an external pushbutton. This causes the current weight, which is normally the empty weight of the container to be stored in memory as an offset. In manual tare, the tare value can be entered manually via the front panel or a computer. For instance, the tare value may be the stated empty weight of a truck or rail car. Pressing the Reset button on the front panel toggles the display between gross weight (total weight on the scale) and net weight (gross weight with tare subtracted).
Load Cell Connection
The load cell signal conditioner, which is normally used with the weight meter, is designed for 4- or 6-wire hookup. In 4-wire hookup, the meter operates in a ratiometric mode to eliminate errors due to supply variations. In 6-wire hookup, it also compensates for variations in transducer lead resistance, thereby allowing long cable runs in changing temperature environments. The built-in isolated 10 Vdc excitation supply can power up to four 350-ohm load cells in parallel.
Easy Scale Calibration
The weight meter is normally set up using a simple two-point calibration method. First, the desired LO IN reading is set to 0, and the desired HI IN reading is set to a desired value. With no weight on the scale, a button is pushed for LO IN. With a known weight on the scale, that button is pushed again for HI IN. The meter then automatically computes scale and offset for readout up to five digits in weight units.
The Micro Weight Meter offers extremely fast read rates. These are ideal for weigh-in-motion systems, setpoint control, and computer interface applications. Concurrent Slope (Pat 5,262,780) is a method of analog-to-digital conversion that allows up to 60 conversions per second, while integrating the input signal over a full line cycle.
An adaptive digital filter can be set for time constants from 17 ms to 9 s, yet responds rapidly to a change in input signal level exceeding a threshold value. The meter can automatically select the best filter setting for maximum noise rejection and minimum response time. Control and interface outputs can be derived from the filtered signal or, for quicker response, from the unfiltered signal. Display of peak value is standard in the Micro Series.
Micro Series meters can be powered from 95-240 Vac ±10% 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.
With Load Cell Signal Conditioner
Error at 25°C
With DC Signal Conditioner
Error at 25°C
With Load Cell or DC Signal Conditioner
Accuracy, Load Cell Signal
0.0030% of reading/°C
2 points using zero weight and known weight
Accuracy, DC Signal
0.01% FS ±1 count
2 points using zero weight and known weight
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
-999990 to 999990 (with selectable fixed right-hand zero)
Count by 1, 2, 5, 10, 20, 50, 100
Four LED lamps
95-240 Vac ±10% 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 ±5%, 100 mA max
10 Vdc ±5%, 120 mA max
24 Vdc ±5%, 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
Weighing the Load on a Truck
This application illustrates some of the capabilities of the Micro Weight Meter. This single meter can power all four 350 ohm load cells of the scale with its 10 V, 120 mA isolated excitation output. Six-wire connection eliminates the effects of lead resistance and allows long cable runs from the control room to the scale.
The five-digit meter can be scaled to display truck weight up to 99,999 lbs with 1 lb resolution or 999,990 lbs with 10 lb resolution. Accuracy is 0.01% of full scale at 25ºC. To avoid the effects of system-level noise, different filter settings as well as “count by” of 1, 2, 5, 10, 20, 50 or 100 with rounding are selectable.
To read out net weight of the load, the truck can first be weighed empty, and this weight can be entered as tare at the push of a button in an auto-tare mode. Or the nominal tare value of the truck can be entered manually. Display of net weight or gross weight is at the push of a button. The gross weight and net weight can be alarmed, be transmitted to a computer via RS232 or RS485, or be transmitted via a 4-20 mA analog signal.
Electrical Connections & Setpoint Offset
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.
The DC signal conditioner board can be utilized to accept preconditioned 4-20 mA or 0-10 V scale signals. In two-wire 4-20 mA transmitter connection, the same two wires are used to apply voltage and carry the output current.
In a repetitive fill operation (as illustrated by example), a setpoint offset of -50 will allow a shutoff setpoint to be set for 1000 and actual shutoff to occur at 950 if it is known that 50 units will still flow following shutoff. An offset can also be applied to emptying operations.