Load Cell, Strain Gauge & Microvolt Digital Panel Meter

20 mV - 500 mV full-scale ranges, 4- or 6-wire connection

Load cell meter by TD Micronic

Features

  • 20, 50, 100, 250 & 500 mV full scale ranges, 1 microvolt sensitivity
  • Zero adjust from -99,999 to +99,999, span adjust from 0 to ±99,999
  • Accuracy of 0.01% of reading ± 2 counts
  • Up to 60 conversions per second
  • Isolated 10 Vdc excitation to power four 350-ohm load cells in parallel
  • 4- or 6-wire hookup to avoid lead resistance effects
  • Universal 85-264 Vac / 90-300 Vdc or 10-48 Vdc / 12-32 Vac power
  • Wide choice of options:
    - 2 or 4 relays, mechanical or solid state (isolated)
    - Analog output, 4-20 mA, 0-10V, or -10V to +10V (isolated)
    - Serial data I/O: Ethernet, USB, RS485, RS232 (isolated)
    - Custom curve linearization, rate from consecutive readings
Description
dc-panel-meter

The load cell, strain gauge and microvolt meter is a 5-digit panel meter with exceptionally high accuracy and stability for use with low-leve signals.

  • Load cell meter operation provides sensitivity down to ±20 mV full scale for use with 2 mV/V load cells at 10V excitation. Ratiometric operation automatically compensates for changes in excitation. The 5 digit display can be scaled 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 ±99,999. Digital scaling and calibration eliminate drift caused by potentiometers in non-microcomputer based meters.
  • DC microvoltmeter operation provides sensitivity down to ±20.000 mV full scale with 1 µV resolution for use with 2 mV/V load cells. A display span of 99,999 counts with sensitivity of 0.2 µV per count can be obtained by applying a digital multiplier of five. A moving average digital filter assures quiet readings in electrically noisy environments.

Meter accuracy in ratiometric bridge operation is 0.01% of reading ± 2 counts. Custom curve linearization, which is available with the optional Extended main board, can extend the working range of load cells. Custom curve linearization also allows greater accuracy to be achieved with lower cost, less linear load cells.

A built-in isolated excitation supply can provide up to 120 mA of current at 10V to power 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.

High read rates at up to 60 or 50 conversions per second while integrating the signal over a full power cycle are provided by Concurrent Slope (US Pat 5,262,780) analog-to-digital conversion. High read rates are ideal for peak or valley capture, real-time computer interface, and control.

Peak and valley values are automatically captured. These may be displayed via a front panel pushbutton command or control signal at the rear connector, or be transmitted as serial data.

Load cell signal conditioner board for TDM digital panel meter Digital filtering is selectable for electrically noisy environments, including a batch averaging filter and an adaptive moving average filter which provides a choice of 8 time constants from 80 ms to 9.6 s. When a significant change in signal level occurs, that filter adapts by briefly switching to the shortest time to follow the change, then reverts back to the selected time constant. In a selectable Auto filter mode, the filter time constant is automatically selected based on detected signal noise.

Scale and offset can be provided by either of two user-selectable 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 no external calibration reference is available.

Auto-tare is standard for weighing applications to subtract the weight of an empty container and may be controlled by an external pushbutton contact closure or a logic signal. Additional capabilities for weighing applications are provided by the weight & scale meter.

Designed for system use. Optional plug-in boards for communications and control include Ethernet and other serial communication boards,dual or quad relay boards, and an isolated analog output board. s may be powered from 85-264 Vac or optionally from 12-32 Vac or 10-48 Vdc. The display is available with red or green LEDs. The 1/8 DIN case meets NEMA 4X (IP65) specifications from the front when panel mounted. Any setup functions and front panel keys can be locked out for simplified usage and security. All power and signal connections are via UL / VDE / CSA rated screw clamp plugs.

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 , whose excitation output is rated 120 mA at 10V. The excitation and sense points of the four bridges are connected in parallel. The load cell outputs will be averaged if the load cells have the same sensititivity in mV/V.

Seat belt tensile strength testing using digital panel meters.
The three meters display Force, Displacement and Speed.

Specifications

DC Microvoltmeter Inputs

Input Range mV Resolution Input Resistance Error at 25°C
±20.000 1 µV 1 GΩ ±0.01% of full scale
±2 counts
±50.000 1 µV
±100.00 10 µV
±250.00 10 µV
±500.00 10 µV

Load Cell Inputs

Full-Scale Input, mV Zero Adjust Span Adjust Input Resistance Error at 25°C
±20.00 0 to ±99,999 1 GΩ ±0.01% of reading
±2 counts
±50.00 -99,999
±100.00 to
±250.00 +99,999
±500.00

DC Microvolts & Load Cell Inputs

Accuracy
Error at 25°C ±0.01% of reading ± 2 counts in ratiometric mode,
±0.01% of full scale ± 2 counts in absolute mode.
Span tempco 0.0015% of reading/°C
Zero tempco 0.1 µV/°C
Load cell linearization Programmable using Extended meter version
Noise Rejection
CMR, DC to 60 Hz 130 dB
NMR at 50/60 Hz 90 dB with min filtering
A-to-D Conversion
Technique Concurrent Slope (Pat 5,262,780)
A-to-D rate 60/s at 60 Hz, 50/s at 50 Hz
Output update rate 56/s at 60 Hz, 47/s at 50 Hz
Display update rate 3.5/s at 60 Hz, 3/s at 50 Hz
Display
Readout 5 LED digits, 7-segment, 14.2 mm (.56"), red or green
Range -99999 to 99999 or -99990 to 99990 (count by 10)
Indicators Minus sign, 2 red LED lamps
Power
Voltage, standard 85-264 Vac or 90-300 Vdc
Voltage, optional 12-32 Vac or 10-48 Vdc
Frequency DC or 47-63 Hz
Power  consumption (typ. with four 350Ω load cells at 10V) 2.4W @ 120 Vac, 2.7W @ 240 Vac, 2.5W @ 10 Vdc, 2.6W @ 20 Vdc, 2.75W @ 30 Vdc, 3.0W @ 40 Vdc, 3.35W @ 48 Vdc
Power Isolation 250V rms working, 2.3 kV rms per 1 min test
Excitation Output (standard)
5 Vdc 5 Vdc ± 5%, 100 mA
10 Vdc 10 Vdc ± 5%, 120 mA
24 Vdc 24 Vdc ± 5%, 50 mA
Output Isolation 50 Vdc to meter ground
Ratiometric operation Automatically compensates for changes in excitation level.
Analog Output (optional)
Output levels 4-20 mA, 0-20 mA, 0-10V, -10 to +10V (jumper selectable)
Current compliance 2 mA at 10V ( > 5 kΩ load)
Voltage compliance 12V at 20 mA (< 60Ω load)
Scaling Zero and full scale adjustable from -99999 to +99999
Resolution 16 bits (0.0015% of full scale)
Isolation 250V rms working, 2.3 kV rms per 1 min test
Relay Outputs (optional)
Relay types 2 Form C contact relays or 4 Form A contact relays (NO) 2 or 4 Form A, AC/DC solid state relays (NO)
Current tatings 8A at 250 Vac or 24 Vdc for contact relays 120 mA at 140 Vac or 180 Vdc for solid state relays
Output common Isolated commons for dual relays or each pair of quad relays
Isolation 250V rms working, 2.3 kV rms per 1 min tes
Serial Data I/O (optional)
Board selections RS232, RS485 (dual RJ11 or RJ45 connectors), USB, Ethernet, USB-to-RS485 converter, Ethernet-to-RS485 converter
Protocols Modbus RTU, Modbus ASCII, Modbus TCP (Ethernet), TDM ASCII
Data rates 300 to 19200 baud
Digital addresses 247 (Modbus), 31 (TDM ASCII),
Isolation 250V rms working, 2.3 kV rms per 1 min test
Signal Connections
Environmental
Operating temperature 0°C to 55°C
Storage temperature. -40°C to 85°C
Relative humidity 95% at 40°C, non-condensing
Protection NEMA-4X (IP-65) when panel mounted
Applications

Sample Load Cell Meter Applications

Auto-Tare 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 automatically tare out the weight of the empty tank and then scale the load cell signals to units of volume, such as liters or gallons.
Capture for 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, RS485, USB or Ethernet.

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