HP 4274A & HP 4275A LCR Meters

© Brooke Clarke 2010

HP 4274A & HP 4275A LCR Meters
Background
Measurement Methods
    4-Terminal Pair
Fixtures
Guarding
HP 1980 Catalog Component Measurement Equipment
Related
Links

Background

While working in the microwave semiconductor business I used many of the H-P Kobe Instrument Division (KID) products.  These are the component test boxes like these Inductance Capactance Resistance (LCR) meters.

The HP 4274A covers the frequency range of 100 Hz to 100 k Hz
The HP 4275A covers the frequency range of 10 k Hz to 10.0 MHz

Measurement Methods

There are a large number of methods of measuring L, C or R, but the 4-port method used in the HP 4274A, HP 4275A and many other LCR meters is the most precise.  For more on impedance measuring methods see the HP/Agilent Impedance Measurement Handbook (5950-3000) written by Makoto Honda and my web page on Impedance.

4-Terminal Pair

The electrical node where all four shields are connected together is "Guard".

DC Resistance in Ohms to Ground

Lc
Lp
Hp
Hc
Shield
10
0
0.8
>200k
Center
100
>30k
open
>200k

a) shields connected together at DUT = guard
b) currents flowing on Hc & Lc shields
c) With proper connections the measurement range is from 1 milliohm to 10 Megohm (or better).
d) WRONG connection, like Kelvin Clips below.
4-Terminal Pair LCR Meter Functional diagram from The Impedance Measurement Handbook.
4-Terminal Pair LCR Meter Functional diagram




There are a large number of fixtures and cable sets for use with the HP/Agilent 4-Terminal PairLCR meters and they are described in the Selection Guide for Impedance Measurements (5965-4792E).

 Fixtures

There are four BNC-male connectors at the lower left of the front panel for connection of a fixture or cable adapter.  Mechanically they seem to be on 22.0 mm pitch.  If you know the actual pitch, Let me know

HP 16047C LCR Test Fixture
HP 16047C LCR Test Fixture
This fixture has an advantage over the 16047D when the leads are either very small in diameter (i.e. arn't stiff enough to push into the spring loaded sockets) or when they are very long.  The bottom of the 16047C looks like the top, i.e. it's open so you can have test leads sticking out the bottom.
HP 16047D Test Fixture
HP 16047D LCR Test Fixture
This is the test fixture that shipped with all the HP LCR meters.  I'm looking for one and both the axial and radial inserts as well as the notched metal plate for doing the zero cal.  Let me know if you have one to sell.
Reproduction HP 16034E SMD Test Fixture
Labeled TH26008A
x

4-Terminal Pair Tweezers
LCR Meter 4-Terminal Pair Tweezers

 Kelvin Clips
LCR meter 4-Terminal Pair Kelvin Clips
These test leads will NOT work correctly because they don't tie the Hc and Lc shields toghther, see fig 3-5d above.
 Home Brew Test Leads
LCR Meter 4-Terminal Pair Home Brew Test Leads
I will modify this cable to add another lead connected to the shield common point, i.e. guard.  Then make up a demonstration of guarding.

Guarding

When the shields of all four test ports are electrically connected, that connection point becomes a "guard" terminal.  By connecting "guard" in a knowledgable way you can eliminate capactiors from the measurement.  These can be real caps or parasitic caps, but either way you can make better measurements.  If you guard something that you don't want to guard you may be making a measurement that's different from what you think you're measuring.

Three test items were made using six each 22 uF caps.

# of 22 uF
Caps in Parallel
Meas by
itself
C1
1
21.75 uF
C2
2
42.03 uF
C3
3
63.3 uF
HP LCR Meter Guard Example
Now when all three are connected in a delta arrangement and the leads of C1 are placed into the test fixture the capactance reads 47.01 uF.
C2 and C3 in series: 1/C23 = 1/C2 + 1/C3 or 25.25 uF
The C2-C3 series connection in parallel with C1 = C1 + 25.25 uF or 47.008  uF (i.e. what's displayed above)

Now when the common point between C2 and C3 is connected to any of the coax shields the reading changes to 21.75 uF, i.e just C1 all by itself.

HP 1980 Catalog Component Measurement Equipment

Component measurement instruments typically are made by the Kobe Instrument Division (KID) of HP.

Model
Description
Remote
4260A
Universal Bridge
na
4261A
LCR Meter
BCD not HP-IB
4262A
LCR Meter
BCD or HP-IB
4265B
Universal Bridge (GR, Boonton?)
na
4271B
1 MHz LCR Meter
HP-IB
4272A
1 MHz Preset C Meter
BCD
4273A
1 kHz Preset C Meter BCD
4274A
Multi-frequency LCR Meter ($7930)
HP-IB
4275A
Multi-frequency LCR Meter ($8720)
HP-IB
4282A
Digital High Cap Meter
HP-IB
4328A
Milliohm Meter
na
4329A
High Resistance Meter
na
4332A
LCR Meter
na
4342A
Q Meter
na
4191A
RF Impedance Analyzer (new 1980) HP-IB
4140A
pA Meter/DC Voltage Source (new 1980)
Semi: I-V and Quasi-static C-V
HP-IB
4800A
Vector/Z/Meter
na
4815A
RF Vector/Z/Meter na
5045A
Digital IC Tester
HP-IB


Related

Impedance
Transmission Line Zo vs. Frequency
HP 4395A Spectrum, Network & Impedance Analyzer
Battery Testers - including internal resistance
Battery Patents
Capacitors table with ESR and Cap measurements for different types
Diodes Understanding Diodes & RF/Microwave Operation
Electronics Page
Electro-optical Gadgets
ESR & Cap Tester
Fly Back Tester (FBTest) - soon
HP4260 Universal Bridge
HP4328A Milliohmmeter
HP4332 LCR Meter
Kelvin Connection Measurements
Inductors - soon
WWVB Loopstick Antenna & C-Max Receiver
Test Equipment
Marconi TF-2700 Universal Bridge
ZM-11/U Capactance-Inductance-Resistance Bridge, line powered
ZM-4 Bridge battery powered

Links

HP Archive - Catalogs
Kenneth A. Kuhn - HP Museum
HP Memory -
Museum of HP Calculators
HP Computer Museum -
HP 9825 Calculator (& 9100) -
Museum of HP Clocks - TVBs site

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page created 8 Oct. 2010.