720A Series Micro-Ohmmeters

Download the 720 Datasheet (pdf format)

The 720A Digital Micro-Ohmmeter
The 720A is an affordable 7 range, four wire Kelvin based digital micro-ohmmeter. Resistance measurements can be made from 10 µOhms to 200 KOhms on seven ranges (9 ranges on 725A) with 4 ½ digit (19999) resolution. The 720A Digital Micro-ohmmeter is used to test electrical resistance on a wide variety of applications such as small motors, transformers, contacts, components, bonds and a host of metal to wire connection integrity (i.e. splices) tests. The unit's high contrast, high intensity LED display is also readable in direct sunlight environments. For automated resistance measurements, the 725A offers an optional BCD Interface, RS232C Serial Interface or GPIB (IEEE-488.2) Talk/Listen Interface. Microprocessor based automatic range selection/control or "Autorange" is also included with either GPIB (IEEE-488.2) or RS232C Interface option.

Need to make a resistance bond measurement?
The battery powered version of the 720A Micro-Ohmmeter makes it simple, and field portable. See below for details.

Resistance Measurements made Easy and Accurate - 720A Series Micro-Ohmmeters
The 720A digital micro-ohmmeter makes 4 terminal Kelvin resistance measurements on a variety of devices including the following:

• Winding resistance and shorted turns of: small motors, alternators, transformers, generators, coils, solenoids, relays, wire spools, chokes and ballasts.
• Contact resistance of: switches, resistive trimmers, mating connectors, relay contacts, circuit breakers.
• Bonding or Connection resistance measurement: any metal to metal connection, crimp lug connections for cables, weld joints, PCB to switch or connector integrity testing, bolted joint resistance of cable connections and earth ground testing.
• Component testing, matching and sorting: Resistors (all types - metal film, wirewounds), pots, strain gauges, shunts, I.C. substrates, thick film circuits, small motors and small transformers, chokes, thermistors, fuses, extruded copper wire, Ni-Chrome wire, all wire alloys, heating elements, printed circuit board clad resistance, plated through holes, plating thicknesses.

An optional rechargeable battery powered version of the 720A Micro-Ohmmeter is available - Ideal for field portable and "On-The-Go" resistance measurement applications. Internal dual battery packs provide hours of mobile field use of the 720A Micro-ohmmeter.

725A - Widerange Micro-Ohmmeter
The 725A Widerange Micro-Ohmmeter has 2 higher level resistance ranges in addition to the 720A, providing the ultimate resistance test versatility. The 725A has the following nine ranges: 200 mOhms, 2.0 Ohms, 20 Ohms, 200 Ohms, 2K Ohms, 20 K Ohms, 200 K Ohms, 2.0 MegOhms and 20 MegOhms. The 725A's higher resistance ranges allow testing of higher value components (i.e. 10 Meg Ohms resistors) and "open circuit" tests (i.e. 20 Megohms) with accuracy. Only the 725A is available with GPIB or RS232C Interface options (Auto-range capability comes with either interface option).

Equipped with a Test Lead Pouch and more ...
Both 720 series ohmmeters come with a Test Lead Pouch (holds the operator manual, Gold Plated 4-Wire Kelvin Clip Leads, Kelvin Mini-probes, extra room for meter accessories, and are configured for 120VAC 60Hz AC power. The 720A can also come configured with dual internal battery pack power for portable field use applications (see Option "DBP" below). Permac also offers over 10 models of Fail-safe/Water Resistant Ohmmeters and a full assortment of 4 wire Kelvin test leads, along with all of the meter accessories, detailed below.

Four Terminal Kelvin - Eliminates Test Lead and connection Contact Resistance Errors
Many critical military, aerospace and industrial applications require resistance characterization of components, bonds and connections at levels well below 1 ohm. In many applications, if a 2 wire (in-series) test lead set is used with an ohmmeter, a large resistance offset error is introduced, often many times in order of magnitude larger than the test items resistance. ALL Permac Micro-ohmmeters use a 4 Terminal or 4 Wire Kelvin Output (2 wires output a constant DC current and 2 wires sense the voltage drop across the resistance being measured) to ensure test lead length and test lead contact resistance are eliminated as sources of measurement error. Even the 720A's 5way binding posts make test wiring connections easy and direct. The 720A Micro-Ohmmeter's gold plated low thermal EMF 5way output posts allow simple connections to spade lugs, banana jacks, or even direct connection to bare wires.

Automated Measurements - Production Test
For automated production-sorting of parts, the 720 series Micro-Ohmmeters comes optionally equipped with a BCD (Binary Coded Decimal) Data Output (Option "101") for use with the 111 "BCD-SORTER" High Go Low Limit Comparator. For automated resistance measurements communicated to a PC controller, the 725A offers several options. A GPIB (IEEE-488.2 - Option "488") Talk/Listen Interface with remote control capability or a RS232C Serial Communication Interface (Option "232"). Microprocessor based Auto-Range control of the 725A is included with either the GPIB or RS232C Interface option

Kelvin Leads, Probes, and Accessories
All 720 series test leads and probes are a minimum 48" length with dual banana termination at the meter end.

Option "300" Gold Plated Four Terminal Kelvin Clip Test Lead Set - The Kelvin Clip ends open large enough to attach to a ½" diameter bolt head.

Option "350" Large Four Terminal Kelvin Clip Lead Set - The large Kelvin Clip ends (PVC composition handles) with attached cables, open to 1¼" for connection to larger lugs, bus bars and bolt heads.

Option "401" Single Point Probe Set - are 4 terminal up to the base of the probe tips. The probe tips have a 0.08" diameter (nail style) shaft for easy probing of socket contacts and miscellaneous recessed parts.

Option "402" 4 Terminal Kelvin Microprobes - similar to Option 401 shown above except each probe has two fine steel tips (sprung loaded) with 0.05" separation.

Option "403" 4 Terminal Kelvin Miniprobes - similar to Option 401 except each probe has two narrower sprung loaded steel tips with 0.18" separation (included with the 720A Micro-Ohmmeter with test lead pouch).

Option "519" Rack Mount Adapter includes support tray, flush panel with cutout and hardware that accommodates a standard NEMA 19" Instrument rack cabinet enclosure.

Option "20C" Ambient Temperature Correction - Ambient temperature changes dramatically affect the resistance of any copper device (i.e. transformer or electric motor). This option automatically compensates for variances in room temperature affecting the resistance of the copper device. The temperature coefficient of resistivity (T.C. = 0.3931% per °C) of copper is used and readings are referenced to a 20°C ambient temperature standard. It doesn't matter if ambient is hot or cold, only that the copper item being measured is also at ambient temperature. Without ambient temperature correction, the same copper device measured on a cold morning will give a dramatically different resistance measurement on a warm afternoon.

Option "DPB" Dual Heavy Duty Rechargeable Battery Pack - Ideal for portable "On the Go" field-use resistance applications, the 720A Micro-Ohmmeter can be operated on internal rechargeable Ni-Cad battery power. Eight internal "D cell" Ni-Cad (5700 mAHR each) provide hours of portable operation/use of the 720A Micro-Ohmmeter. The Option "DBP" also includes the 120 VAC line powered battery charger, the internal battery packs can be recharged up to 1000 times providing years of portable use.

Specifications
Accuracy: (1 year 18°- 28°C) ± 0.02% of reading ± 0.02% of range for 200 milliohm through 200 Kohm ranges. (Model 725A upper ranges ± 0.5% of reading ± 0.5% of range for the 2 MegOhm range. ± 1% of reading ± 1% of range for the 20 MegOhm range).
Display: 4½ digit (19999) LED - 20,000 counts readable in daylight
Terminal Configuration: Four-wire Kelvin
Overload Indication: Display flashes
Maximum Input: 250 VDC or peak AC without damage
Operating Temperature Range: 0°C to 50°C
Temperature Coefficient: ±.002% per °C (from 0°C to 15°C and 35°C to 50°C)
Conversion Rate: Approximately 3 per second
Power: 115 VAC 50-60 Hz
Size: 235mm/9" D x 254mm/10" W x 76mm/3" H
Weight: 1.6 KG/3.5lbs NET 3 KG/6.5 lbs shipping