Ohmmeter for Resistance in Ohms

High accuracy & high speed for production environments, plus transmitter & control outputs

Ohmmeter by TD Micronic

Features

  • Five jumper-selectable resistance ranges of 20.000 ohm to 200.00 kohm
  • Fixed factory-special ranges of 2.0000 ohm or 2.0000 Mohm
  • 0.1 milliohm resolution on 2 ohm scale for contact resistance measurements
  • 2, 3 or 4-wire connection with lead resistance compensation
  • Up to 60 conversions per second
  • 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)
    - Extended version to linearize and scale nonlinear reistance sources
Description

The Ohmmeter is ideal for high-speed, high-accuracy resistance measurements in a production environment, such as contact resistance measurements. It is factory calibrated for five jumper selectable resistance ranges from 20.000 ohm to 200.00 kohm. Fixed, factory-special ranges of 2.0000 ohm or 2.0000 Mohm are also available. Accuracy is an exceptional ±0.01% of reading ± 2 counts. Resolution is one part in 20,000. In the 2 ohm range, resolution is 0.1 milliohm, making the meter ideal for contact resistance measurements.

An Extended ohmmeter version is ideal for use with nonlinear sensors whose output is a changing non-linear resistance. Extremely accurate custom curve linearization is provided by curvilinear spline fits, and the reading can be scaled in software to read in user-selected engineering units of measure.

Meter connections can be via 2, 3 or 4 wires. With 4-wire hookup, 2 wires are used for excitation and two separate wires are used to sense the voltage across the resistance to be measured, thereby eliminating any lead resistance effects. With 3-wire hookup, the meter senses the combined voltage drop across the resistance to be measured plus two excitation leads. It also senses the voltage drop across one excitation lead, and then subtracts twice this voltage from the combined total. This technique effectively subtracts lead resistance if the excitation leads are the same.

All resistance ranges are digitally calibrated at the factory, with calibration factors stored in EEPROM on the signal conditioner board. This allows ranges and signal conditioner boards to be changed in the field without recalibrating the meter. If desired, the meter can easily be calibrated using external standards plus scale and offset in software.

Using a meter with a current shunt 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 high-throughput manufacturing processes. Peak and valley values are automatically captured and may be displayed via a front panel pushbutton command or a control signal at the rear connector, or be transmitted as serial data.

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 anisolated 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.

Multiple relay operating modes are selectable in software. One of these is band deviation setpoint operation, where a deviation limit (such as 50 counts) is set up around both sides of the setpoint. The relay closes (or opens) when the reading falls within the deviation band, and opens (or closes) when the reading falls outside of this band. This mode sets up a passband around the setpoint and is often used for component testing.

Resistance Measurement with Excitation & Lead Compensation

Ohmmeter hookup can be via 2, 3 or 4 wires to the J5 connector. The meter applies a fixed excitation current for each resistance range.
4-wire connection to resistance signal condidioner In 4-wire hookup, different pairs of leads are used to apply the excitation current and sense the voltage drop across the unknown resistance, so that the IR drop across the excitation leads is not a factor.
3-wire connection to resistance signal condidioner In 3-wire hookup, the meter senses the combined voltage drop across the unknown resistance plus two excitation leads. It also senses the voltage drop across one excitation lead, and then subtracts twice this voltage from the combined total. This technique effectively subtracts all lead resistance and compensates for ambient temperature changes if the two excitation leads are identical.
2-wire connection to resistance signal condidioner In 2-wire hookup,the meter senses the combined voltage drop across the unknown resistance and both lead wires. The voltage drop across the lead wires can be measured by shorting out the resistance during meter setup, and this voltage is then automatically subtracted from the combined total. However, changing resistance of the lead wires due to ambient temperature changes will not be compensated.

QA Application with Relay Option in Passband Mode

Deviation mode relay operation for digital panel meters and counters
A deviation limit (50 mohm in this example) is set up around both sides of a setpoint. The relay closes (or opens) when the reading falls within the deviation band, and opens (or closes) when the reading falls outside of this band. This mode sets up a passband around the setpoint and can be used for contact resistance testing.
Specifications
Range Resolution Accuracy Excitation Current ***
0-2.0000 ohm ** 0.1 mohm ±0.01% of reading
± 2 counts
5 mA
0-20.000 ohm * 1 mohm 5 mA
0-200.00 ohm * 10 mohm 500 µA
0-2000.0 ohm * 100 mohm 50 µA
0-20000 ohm* 1 ohm 5 µA
0-200.00 kohm * 10 ohm 500 nA
0-2.0000 Mohm ** 100 ohm 500 nA
* Jumper-selectable, precalibrated range.
** Factory-set fixed range.
*** The applied excitation current is sensed by the meter, which operates in a ratiometric mode and automatically compensates for any changes in excitation.

Display
Readout 5 LED digits, 7-segment, 14.2 mm (.56")
Color Red or green LED
Indicators 2 red LED lamps
Accuracy
Accuracy at 25°C ±0.01% of reading ± 2 counts
Span tempco ±0.003% of reading/°C
Electrical
Connection 2, 3 or 4-wire
Max applied voltage 100 mV
Overvoltage protection 125 Vac
Open sensor indication Flashes full-scale
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
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 (typical, base meter) 1.2W @ 120 Vac, 1.5W @ 240 Vac, 1.3W @ 10 Vdc, 1.4W @ 20 Vdc, 1.55W @ 30 Vdc, 1.8W @ 40 Vdc, 2.15W @ 48 Vdc
Power Isolation 250V rms working, 2.3 kV rms per 1 min test
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
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

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