Delta Electronics Digital RF Ammeter Systems

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Summary

The Model DTCA Digital RF Ammeter provides AM broadcasters and other high power RF operators with an accurate, reliable and high resolution digital instrument for measuring RF current.

The 100:1 dynamic operating range enables RF current measurement over a 10,000:1 power range and allows the broadcaster to use a single instrument for day, night, pre-sunrise and post-sunset operating modes. The ammeter system uses the Model TCT toroidal current transformer to provide a sample voltage proportional to the RF current. The ammeter converts this RF voltage to a DC voltage which is applied to a 3-1/2 digit display. The reflective liquid-crystal display with 0.7 inch character height provides a high resolution and easily readable RF current magnitude indication. Over the AM broadcast band, the DTCA provides an accuracy of better than 2% with a resolution better than 1/100 of the RF current. The DTCA indicates the average RMS current independent of amplitude or phase modulation. The dual remote outputs of 2.15 VDC full scale and 10.0 VDC full scale easily interface with existing remote monitoring equipment.

The DTCA circuit design is inherently wide band to extend RF current measurement capabilities for LF applications at frequencies as low as 20 kHz and for HF applications at frequencies up to 5 MHz. The DTCA circuit is temperature compensated to enable rated accuracy performance over a -40°C to +50°C temperature range.

Features

Description

The Digital RF Ammeter system comprises a toroidal current transformer unit, a detector/display unit and an interconnecting coaxial cable. Depending on the RF conductor voltage, the transformer unit may be either the TCT-N (10 kVRMS rating) transformer, the TCT-N-HV (20 kVRMS rating) transformer or the TCT-N-XHV (42.4 kVRMS rating) transformer. These transformer voltage ratings are the RMS equivalent of the peak modulation voltage. Within each TCT type, several versions are available depending on the RF current magnitude. The TCT provides an RF voltage sample directly proportional to the current. The voltage sample is applied to the detector/display unit by a 50 ohm coaxial cable. The detector circuit provides a 50 ohm load resistance for proper termination. The detector circuit converts the RF voltage sample to a DC voltage which is applied to the digital display. The autoranging input attenuator and precision detector circuits provide accurate RF current measurement over the 100:1 operating range. The 3-1/2 digit/2000 count liquid-crystal display provides a high resolution digital RF current measurement which is stable over amplitude and phase modulation variations. Dual remote outputs of 2.15 VDC full scale and 10.0 VDC full scale easily interface with existing remote monitoring equipment. The front panel switch controls the local operation of the ammeter. In the off position, the detector circuit input is disconnected from the RF input for lightning protection. The ammeter operates from an external 18 to 28 VDC, 80 mA power supply (TCA-PS2 or equivalent) or 18 VAC, 200 mA power module.

The digital RF Ammeter series encompasses several models to provide RF current measurement over the range from 0.1 to 160 Amperes full scale. The 100:1 dynamic operating range enables RF current measurement over a 10,000:1 power range. Since the ammeter indicates the average RMS current independent of modulation, it is practical to use the ammeter up to the full scale value.

The standard interconnecting coaxial cable length is six feet. Longer coaxial cable lengths and double shielded coaxial cable are optionally available for any DTCA system for high RF field conditions and for RF radiation exposure reduction.

Ammeter Accuracy and Calibration

The Digital RF Ammeter Systems are capable of measuring RF current with excellent accuracy. The accuracy specification of 2% of reading is guaranteed over a temperature range of ­40°C (­40°F) to +50°C (+122°F) and over a frequency range of 500 kHz to 2000 kHz.

Every Digital RF Ammeter is calibrated at a frequency of 1 MHz at the Delta laboratory. The flat frequency response and compensated temperature characteristics of the ammeter assure accurate current measurement. The calibration of the ammeter is warranted for a period of one year under normal use conditions. Excluding damage due to lightning, Delta will recheck the calibration and make repairs, if necessary, without charge during this period. These services are available at a nominal charge at any time thereafter.

Meter Nomenclature

The DTCA Digital RF Ammeter series includes a wide variety of operating current ranges and current transformer conductor voltage ratings which are uniquely defined in the model designation system. Standard current ranges are 0.1 to 10A, 0.2 to 20A, 0.4 to 40A, 0.8 to 80A and 1.6 to 160A. Each of these five current ranges are available with current transformer conductor voltage ratings of 10 kV, 20 kV and 42.4 kV.

DTCA-N: The standard series is supplied with a current transformer rated for operation at conductor voltages as high as 14 kV peak (10 kVRMS). The transformer provides a 1.25″ diameter clearance hole for the antenna connector. A 0.38″ to 0.5″ diameter tubular conductor contained in the clearance hole provides optional voltage capability. The TCA-LS-8 and TCA-LS-11 line sections which increase the voltage rating by approximately 50% are available as a factory installed option.

DTCA-N-HV: The suffix “HV” appended to any of the DTCA series model numbers specifies that the current transformer supplied with the meter is the high voltage type rated for operation at conductor voltages as high as 28 kV peak (20 kVRMS). The transformer provides a 3.38″ diameter clearance hole for the antenna conductor. A 0.75 to 1.0″ diameter tubular conductor centered in the clearance hole provides maximum voltage capability. Corona rings which increase the voltage rating by approximately 5% are available as a factory installed option.

DTCA-N-XHV: The suffix “XHV” appended to any of the DTCA series model numbers specifies that the current transformer supplied with the meter is the extra high voltage type rated for operation at conductor voltages as high as 60 kV peak (42.4 kVRMS). The transformer provides a 6.0″ diameter clearance hole for the antenna conductor. A 2.0 to 2.25″ diameter tubular conductor centered in the clearance hole provides maximum voltage capability.

 

AVAILABLE MODELS

Current Range
(ARMS)

Current Transformer Voltage Rating

10 kVRMS
DTCA-N

20 kVRMS
DTCA-N-HV

42.42 kVRMS
DTCA-N-XHV

0.1 to 10 A

DTCA-10

DTCA-10-HV

DTCA-10-XHV

0.2 to 20 A

DTCA-20

DTCA-20-HV

DTCA-20-XHV

0.4 to 40 A

DTCA-40

DTCA-40-HV

DTCA-40-XHV

0.8 to 80 A

DTCA-80

DTCA-80-HV

DTCA-80-XHV

1.6 to 160 A

DTCA-160

DTCA-160-HV

DTCA-160-XHV

 

DIGITAL RF AMMETER ACCESSORIES

TCA-PS2

DC Power Supply, 120/240 VAC 50/60 Hz Input, ±15 VDC/100 mA and 24 VDC/500 mA outputs

TCA-LS

Conductor Bushing (Increases standard TCT transformer voltage rating to 15 kVRMS)

TCA-MB

Mounting Bracket (Mounts one or two standard TCT transformers or one meter unit)

TCA-TS

Transient Suppressor Assembly (Type N T-Adapter with connector mounted suppressor)

TCA-RFR

EMI/RFI Shielded Enclosure (Houses DTCA unit and protects from dust, dirt, oil and water)

Technical Specification

Technical Specification

Frequency Range: 0.5 to 2 MHz at rated 2% accuracy, 20 kHz to 5 MHz with 5% accuracy
Operating Range: 100:1
Standard RF Current Ranges: DTCA-10: 0.1 to 10 A
DTCA-20: 0.2 to 20 A
DTCA-40: 0.4 to 40 A
DTCA-80: 0.8 to 80 A
DTCA-160: 1.6 to 160 A
Indicating Instrument: 3 1/2 digit/2000 count reflective LCD display with 0.7 inch (17.8 mm) character height
Accuracy: Better than 2% of reading. Accuracy may be reduced if RF currents induced by other stations are 5% or greater than the current to be measured.
Resolution: One part in 100 minimum, one part in 1200 maximum
Remote Outputs:1) 2.15 VDC full scale, 16K source compatible with Delta Model TCA-IBA Buffer amplifier, output linear with RF current2) 10.0 VDC full scale, 16K source, output linear with RF current
Power Requirement: 120/240 VAC primary/18 VAC @ 200mA secondary power module (supplied) or 18 to 28 VDC, 80 mA power supply (TCA-PS2 or equivalent)
Range Selection: Automatic
Current Transformer: Delta Model TCT, TCT-HV or TCT-XHV for AM broadcast band (500 kHz to 2 MHz); Suitable transformer required for lower/higher frequencies
Interconnecting Cables: Standard six foot, 50 Ohm coaxial cable supplied to connect transformer unit to detector/display unit. Longer cable length and double shielded coaxial cable are optionally available.
Conductor Voltage to Ground (RMS Equivalent of Peak Modulation Voltage):
DTCA-N Series: 10 kVRMS
DTCA-N-HV Series: 20 kVRMS
DTCA-N-XHV Series: 42.4 kVRMS
Temperature Range: -40degreesC (-40degreesF) to +50degreesC (+122degreesF)
Modulation Characteristics: Indicates ave

 

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