Fluke 85RF Operating Manual

Page 1

85RF II

High Frequency Probe

Instruction Sheet

Introduction

The 85RF II High Frequency Probe (the Probe) transforms a dc voltmeter into a high frequency (100 kHz to 500 MHz) ac voltmeter. Conversion from ac to dc is done on a one-to-one basis and includes a range of 0.25 V rms to 30 V rms. The Probe’s dc output is calibrated to be equal to the rms value of a sine wave input.

Safety

Symbol Description

W X

To prevent possible electrical shock, fire, or personal injury:

• Examine the case before you use the Product.

Look for cracks or missing plastic. Carefully look at the insulation around the terminals.

• Limit operation to the specified measurement

category, voltage, or amperage ratings.

• Do not touch voltages >30 V ac rms, 42 V ac

peak, or 60 V dc.

• Do not use the Product around explosive gas,

vapor, or in damp or wet environments.

• Do not use and disable the Product if it is

damaged.

• Use the Product only as specified, or the

protections supplied by the Product can be compromised.

• Do not exceed the Measurement Category (CAT)

rating of the lowest rated individual component of a Product, Probe, or accessory.

• Keep fingers behind the finger guards on the

Probes.

• Do not connect directly to mains.

See Instruction Sheet.

Hazardous voltage.

Do not dispose of this product as unsorted municipal waste. Go to Fluke’s website for recycling information.

WXWarning

PN 4096837 September 2011, Rev. 1, 12/11

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Specifications

AC to DC ratio: 1:1

Ratio accuracy: (at 25 MHz and loaded with 10 Me )

Above 0.5V: ± 0.5 dB Below 0.5V: ± 1.0 dB Add ±0.2 dB in RF fields of 1 V/m to 3 V/m

Frequency response: (Relative to 25 MHz)

100 kHz to 80 MHz ±0.5 dB *80 MHz to 200 MHz ±2.0 dB *200 MHz to 300 MHz ±3.5 dB *300 MHz to 400 MHz ±4.5 dB *400 MHz to 500 MHz ±5.5 dB *Referred to high and low inputs at Probe tip.

Extended frequency response:

Useful for relative measurements from 20 kHz to 700 MHz.

Response:

Responds to the peak value of an input and is calibrated to read rms value of a sine wave.

Voltage range: 0.25 V rms to 30V rms

Maximum input voltage: 30 V rms, 200 V dc

Input capacitance: Approximately 9 pF

Temperature range:

Operating: +10 °C to +35 °C Storage: -40 °C to +75 °C

Humidity: <90 % R.H.

Output connector:

Fits standard 0.75 inch dual banana connectors

Accessory:

BNC to Probe Adapter, P/N 574756

Pollution degree: 2

Operating altitude: 3000 m

Warranty: 1 year

Voltmeter Compatibility

The 85RF II can be used with a dc voltmeter that has an input resistance of 10 Me, ±10 %. Voltmeters with higher input resistances are usable if an external shunt is put across the input terminals. The shunt value is set to decrease the input resistance to 10 Me.

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Operation

To operate the 85RF II Probe:

1. Connect the Probe output to a compatible voltmeter with an applicable shunt (if necessary.) The Probe’s output low must be connected to voltmeter low.

2. Set a voltage range (1 V dc reading for each 1 V rms Probe input).

3. Connect the input low (clip lead or tip shield) to earth ground.

WXWarning

Input low is intended to be connected to earth ground. To prevent electrical shock, input low (clip lead or tip shield) must be connected to potentials of less than 30 V ac, 42 V peak, or 60 V dc.

Frequency Measurements

Frequencies less than 100 MHz

To measure frequencies less than 100 MHz:

1. Ground the 4-inch clip lead supplied with the Probe.

2. Touch the Probe tip to the circuit under test.

Frequencies greater than 100 MHz

To measure frequencies greater than 100 MHz:

1. Ground the 4-inch clip lead supplied with the Probe.

2. Touch the Probe tip to the circuit under test.

Note Measurements above 100 MHz must be made with minimum cable lengths and a terminated 50 One inch or less of non-terminated coaxial cable (such as a BNC adapter and 50 measurements up to 300 MHz.

termination) is required for

system.

Frequencies greater than 300 MHz

To measure frequencies greater than 300 MHz:

1. Ground the 4-inch clip lead supplied with the Probe.

2. Touch the Probe tip to the circuit under test.

Measurements above 300 MHz must have the Probe tip and tip shield (input high and low) touch the circuit under test to realize the rated accuracy of the Probe. Lead lengths less than 1-inch can cause substantial errors.

Note

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WCaution

To prevent Probe damage, the dc component of the input signal (includes transients) must not be more than 200 V dc. Maximum Probe input is 30 V ac rms and 200 V dc. Measurements of an ac signal riding a dc voltage can be made up to 200 V dc. The input capacitor charges to the peak value of ac plus dc. If the dc level is then changed by more than 200 V dc, the transient can possibly damage the Probe. The chance of damage can prevented if the input capacitor is discharged at the end of each measurement. Momentarily touch Probe tip to the ground clip to discharge the capacitor.

Performance Test/Calibration

The performance and calibration test is a verification test to make sure that the 85 RF II is functional and correctly calibrated. Use the procedure as an acceptance test and/or calibration procedure (the Probe has one adjustment which is R2). The recommended calibration interval is one year.

If the Probe cannot be calibrated to the specifications in this document, the Probe could be damaged and require replacement or repair. Contact Fluke for instructions.

1. Configure the equipment as shown in Figure 2. Use the leveled sine function of the scope output to set the AC Calibrator signal generator for 1 V rms at 25 MHz and the DMM to measure 1 V dc.

Note

AGND

220P

MP1 E1

STANDOFF CLIP

CR2

BAT41ZFILM

CR1

BAT41ZFILM

Figure 1. Schematic Diagram

330P

1.82M

500K

WP2

1.3M

CR3

1N4448W

WP1

gsk001.eps

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Required Equipment List

The following equipment (or equivalent) is required for testing the performance of the 85RF II:

Equipment Type Recommended Model

AC Calibrator Fluke 5520A-SC600

50-Ohm Feed Thru Termination

BNC Jack to Banana Plug Adapter

BNC to Probe Adapter

Digital Multimeter, 3-1/2 Digit (DMM)

BNC Jack to Jack Adapter

Fluke 85RF Probe under test

JFW Industries P/N 50L-001

Pomona P/N 1269

Fluke P/N 574756

Fluke 87V

Pomona 3283

gsk002.eps

Figure 2.

Equipment Configuration for Performance Test

2. The DMM will read between 0.950 V dc and 1.050 V dc. If the Probe is functional but is not in these limits, disassemble the Probe (refer to the “Probe Disassembly” Section in this Instruction Sheet) and adjust R2 for a DMM measurement between 0.990 V dc and 1.010 V dc. Reassemble the Probe.

3. Move the unit in test to the Normal output of the calibrator and decrease the output level to 0.250 V rms and 1 MHz. The DMM will read between 0.223 V dc and 0.280 V dc.

4. Set the AC Calibrator to STDBY, decrease the frequency to 100 kHz and increase the voltage to 30 V ac rms. (Do not increase the voltage to more than 30 V ac.)

5. Set the AC Calibrator switch to OPER. The DMM will read between 28.3 V dc and 31.8 V dc.

6. Move the unit in test back to the scope output and set the level sine to 1 V rms 160 MHz. The DMM will read between 0.9 V dc and 1.12 V dc. Increase the frequency to 450 MHz. The DMM will read between 0.562 V dc and

1.780 V dc.

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Probe Disassembly

Use this procedure to access the internal components of the Probe which includes the R2 calibration adjustment.

1. Remove the bend relief screw and move it away from the Probe.

2. Remove the Probe cover. You will see the R2 adjustment.

3. Carefully remove the Probe tip from the front of the Probe with pliers.

4. Remove the ground lead screw from the Probe body.

5. Lift the rear of the printed circuit board up ¼-inch and pull it away from the Probe tip.

6. To reassemble the Probe, do the steps in this procedure backwards (start with step five and end with step one.) Make sure that the gold pin on the front of the printed circuit board aligns correctly in the Probe tip and that the ground-lead nut is aligned with the hole in the Probe body.

How to Clean the Probe

WXWarning

For safe operation and maintenance of the product, remove the input signals before you clean the Product.

Use a soft cloth dampened in a weak solution of detergent and water to clean the 85RF II. Do not use solvents.