Time Electronics 1024 Manual de usuario

User Manual

1024

DC Current Calibrator

Version 1.2

09/22

Time Electronics Ltd

Unit 5, TON Business Park, 2-8 Morley Road,

Tonbridge, Kent, TN9 1RA, United Kingdom.

T: +44 (0) 1732 355993 | F: +44 (0) 1732 350198

mail@timeelectronics.co.uk | www.timeelectronics.com

Nothing from this manual may be multiplied, or made public in any form or manner, either

electronically or hard copy, without prior written consent from Time Electronics Ltd.

This also applies to any schematics, drawings and diagrams contained herein.

This manual provides operating and safety instructions for the Time Electronics product.

To ensure correct operation and safety, please follow the instructions in this manual.

Time Electronics reserves the right to change the contents, specifications and other

information contained in this manual without notice.

Time Electronics

1024 DC Current Calibrator User Manual

Contents

1Introduction.......................................................................................................................................4

1.1 Description................................................................................................................................................ 4

1.2 Specifications ........................................................................................................................................... 5

2Operation...........................................................................................................................................6

2.1 Front Panel Controls................................................................................................................................. 6

2.2 Operating Procedure ................................................................................................................................ 8

2.3 Output Noise............................................................................................................................................. 9

2.4 Mains Power Unit ................................................................................................................................... 11

3Constructional Layout Details....................................................................................................... 13

3.1 Chopper amplifier module....................................................................................................................... 13

4Repair and Recalibration ...............................................................................................................14

4.1 Repairs ................................................................................................................................................... 14

4.2 Recalibration........................................................................................................................................... 14

5Warranty and Servicing.................................................................................................................. 17

Time Electronics

1024 DC Current Calibrator User Manual

1Introduction

1.1 Description

The 1024 is an accurate and stable battery/mains powered DC current calibrator, sourcing up

to 99.999 mA in 5 ranges with a resolution up to 0.1 nA. This enables the instrument to be

portable and convenient for use in the laboratory, field, or industry.

The null balance system enables the 1024 to be used for making accurate current

measurement in addition to its basic function as a calibrator. Operation is by backing the

current source output against the current to be measured, with the difference being displayed

on a sensitive centre zone null meter. At the null point, there is no voltage drop across the

1024.

The 1024’s outstanding accuracy and stability is achieved by using an LTC advanced

subsurface Zener bipolar reference source; this features a very low drift of 2ppm/°C max TC,

coupled with the use of low temperature coefficient precision metal film resistors of less than

10ppm/°C, this ensures that the accuracy and stability of the initial calibration is maintained for

the calibration period. Excellent zero stability is ensured by the use of a high performance FET

chopper amplifier system.

Operation is from the internal re-chargeable battery pack, or mains supply. A front panel

indicator that also serves as a supply on-off display, monitors the battery charge condition.

The battery indicator shows a red light when the battery pack should be recharged. Charging

is performed by the instruments own internal charger/power supply. Simply plugging the 1024

into a mains supply will charge the batteries. Operation of the 1024 may be continued when

plugged into the mains supply.

Applications include calibration and testing of current sensitive transducers; calibration and

linearity tests on digital and electronic current meters; and semiconductor parameter

measurements e.g. diode conduction voltages at specified current levels.

Time Electronics

1024 DC Current Calibrator User Manual

1.2 Specifications

Output: 0 to 99.999 mA in 5 ranges

0 to 99.999 mA in 1 µA steps

0 to 9.9999 mA in 100 nA steps

0 to 999.99 μA in 10 nA steps

0 to 99.999 μA in 1 nA steps

0 to 9.9999 μA in 0.1 nA steps

Accuracy: ± 0.02% of setting, + ± 0.005% of range, + ± 0.2 nA

Compliance Voltage: 15 V with new batteries or mains power

(11 V with minimum allowable battery level)

Regulation: Load: Better than 5 ppm/V

Supply: Better than 5 ppm/V

Output polarity: Positive or negative switch selected. A centre off position

provides an open circuit on the output terminals

Out of limit warning: A front panel indicator provides a warning of insufficient

drive voltage

Output stability: Less than 30 ppm/°C (0°C to + 50°C)

Less than 10 ppm per hour at constant temperature

Less than 75 ppm per 6 months

Output noise: 99.999, 9.9999 mA & 999.99 µA ranges: less than 5 ppm of FS

99.999 and 9.9999 µA ranges: less than 10 ppm of FS ± 0.1 nA

Null sensitivity: Adjustable from ± 25 mA to ± 25 µA FS via front panel

control. Maximum resolution is 0.5 µA.

Power supply: Time Electronics power unit type PU2 which is housed in the

rear of the 1024. The PU2 will power the 1024 direct from the

mains or an internal rechargeable battery pack. The battery is

automatically charged when mains power is connected.

Dimensions: W 217 x H 160 x D 193 mm

Weight: 3.3 Kg

Time Electronics

1024 DC Current Calibrator User Manual

2Operation

2.1 Front Panel Controls

1. Output terminals

The 1024 output current is from two front panel 4 mm safety terminals which are suitable for

wire compression, 4mm spade, and 4mm shrouded or standard plug insertion. The output

current will flow from the + (red) terminal when the polarity switch is ‘normal’ (positive).

2. Case terminal

The isolated 4 mm case terminal is connected only to the instrument case. The case provides

an overall electrostatic screen for the 1024 and can be earthed as required to improve

rejection of noise pick-up.

3. Power On-Off

A toggle switch interrupts the internal DC supply line to the circuitry (off or on).

Indication of supply condition is provided by the battery level indicator.

4. Output Polarity

A change-over toggle switch enables the output current polarity to be reversed. A centre ‘off’

position provides an open circuit on the output terminals.

Switch identification: Normal-Off-Reverse equates to Positive-Off-Negative.

Time Electronics

1024 DC Current Calibrator User Manual

5. Battery Level

The battery (or mains power supply PU2) output is continuously monitored on a front panel

indicator which also serves as a supply ‘on-off’ indication. A red illumination indicates when

the batteries need recharging, green indicates the unit is ready for use.

Note: The battery pack will continue to charge as long as the mains supply is connected.

6. Range Selector Knob

One of the five output ranges can be selected.

7. Digit Switches

A 5-decade thumbwheel switch enables the output current level to be set with a resolution of

0.01% of full scale.

8. Voltage Limit

An LED indicator shows when the 1024 is unable to supply sufficient drive voltage to maintain

the set output current.

Example: The 1024’s maximum drive voltage (voltage capability) is 15 V. This means that it

is able to supply a current of 1 mA into 15 kΩbut NOT 1 mA into 16 kΩ. In the latter condition

the voltage limit indicator would display.

The above is an example, but the same applies for any product of current & load resistance

that exceeds 15 V. Non-resistive loads are still bound by the same output voltage limit with

the indicator displaying when the voltage at the output terminals reaches approx. 15 V.

Note: When the 1024 is operated from partly discharged batteries, the voltage limit is reduced to a minimum of

about 10 V for nearly fully exhausted cells. The battery level indicator gives a clear indication of battery state.

9. Null Meter

Scaled 25-0-25 for displaying the difference current when the 1024 is used in the null mode.

10. Sensitivity Control

A continuously variable control for adjusting the null meter sensitivity, range of adjustment is

from 25mA minimum (fully anticlockwise) to 25µA maximum (fully clockwise).

11. Source - Null Switch

A two-position toggle switch selects the mode of operation. In the SOURCE position the 1024

operates as a current source while the null position allows measurement of current.

Important Note: Under no circumstances must an additional voltage be connected in series with the 1024 output

in an attempt to increase the voltage capability. This practice will cause damage to this 1024’s output circuitry.

Under certain conditions the voltage capability can be increased to a maximum of 50 V. This requires special circuit

modifications and is only applicable to certain ranges. Please consult Time Electronics for information.

Time Electronics

1024 DC Current Calibrator User Manual

2.2 Operating Procedure

2.2.1 Normal Operation

Operation of the 1024 is self-explanatory from the front panel controls and specifications. It is

important to understand the 1024’s voltage capability and voltage limit indicator to ensure that

your requirement is within the limit. It is also important to read the section on output noise if

your requirement is for current levels of less than a few tens of microamps.

When the 1024 is operating from batteries and required to supply currents in excess 10 mA it

is important to check the battery condition with the load connected since the battery’s

condition may be adequate for sourcing low output currents but not higher current.

Measurement of an unknown current:

1) Select ‘NULL’ position on the front panel function switch.

2) Select ‘NORMAL' output.

3) Adjust ‘SENS’ for minimum sensitivity (fully anticlockwise).

4) Select range consistent with the expected current to be measured.

5) Connect the unknown current to the terminals in the same polarity i.e. unknown current

flows into the + Ve terminal.

6) Adjust digit switch and sensitivity control for null balance (0) on meter as required.

7) When balance at required sensitivity is reached the unknown current is equal to the digit

switch setting.

Overload conditions

The 1024 can withstand indefinitely either short or open circuit on the output terminals.

Overload conditions can easily result if any attempt is made to drive current into the 1024 by

applying a voltage to the output terminals. In most cases this will cause the output fuse (See

Section 2.5) to blow but can still cause damage to the output circuitry.

Time Electronics

1024 DC Current Calibrator User Manual

2.3 Output Noise

a) Inherent Noise

The electrical noise on the output current consists of chopper intermodulation, thermal noise

and random variations. These are generated inside the 1024 and originate from the active

circuitry. At current levels of greater than about 1mA the noise fluctuations are those of the

accurate voltage reference circuitry.

At currents below a few hundred microamps it becomes difficult to differentiate between the

1024 inherent noise and picked-up noise.

b) Noise Pick-up

In addition to the inherent noise from the 1024 circuitry the output can contain fluctuations

which originate from outside sources.

As with voltage signals the effects of noise on current signals are usually measured as a

fraction of the signal (in % or PPM) and in general this fraction becomes larger as the signal

level is reduced.

Care must be taken in attempting to understand the cause and effect of noise pick-up on

precision current sources such as the 1024, and it is not proposed that this manual should

cover them in detail.

It is important when confronted with a problem of noise pick-up to stop and think logically

about the cause and effect, as a good deal of time can be wasted by indiscriminate screening

and earthing.

This is particularly important when dealing with current signals since many of the effects are

the exact opposite from those for voltage signals. For example, earthing one side of a voltage

signal may reduce the noise pick-up but earthing the same side of a current signal may

increase the pick-up.

Before looking at possible sources of noise pick-up it is also important to consider the way in

which the presence of noise is being detected. In many cases it will appear as an incorrect

readout.

Special care must be taken if additional equipment (such as an oscilloscope or DMM) is

connected for the detection of noise - there is a possibility that this can introduce further noise.

Two of the more common causes of noise pick-up are discussed below. The actual level of

pick-up cannot be predicted and will depend on a number of factors.

Time Electronics

1024 DC Current Calibrator User Manual

1) 50-60 Hz Mains Supply: This is probably the largest single source of noise pick-up. The

noise from this source can be divided roughly into two parts.

a) 50-60 Hz Signal pick-up - is generally caused by the close proximity of unscreened

mains cables or mains powered equipment. The effects of this type of noise can

usually be considerably reduced by correct screening and earthing.

Important Note:

When the 1024 is operated from mains power, special attention should be paid to the possibility of noise pick-up

occurring. Battery operation is recommended for applications requiring the lowest noise pick-up condition.

b) Transient Signal pick-up - is generally caused by heavy load switching on the mains

from equipment such as electric motors, electric ovens, etc. Its effect on the 1024 is to

cause a transient variation in the output which can last longer than the actual duration

of the noise.

This is because the 1024 has been transiently over-loaded and needs time to recover.

The noise is often in the form of a burst of radio frequency energy which in addition to

being carried in mains cables is also radiated into the atmosphere.

It is often difficult to detect its presence due to its transient nature and short duration

(down to a few 10's of microseconds). The effects of this sort of noise on radio and

television reception are well known and a transistor radio is often a useful tool in

locating the source of the noise.

This type of noise often covers a very wide spectrum of frequencies and the most

effective solution is to locate its source and provide suitable filtering - such as

conventional capacitor suppression on arcing contacts.

2) Common Mode Noise: Additional noise and variation of the output current can be caused

by large common mode voltages. These occur when the 1024 is used to calibrate any input

which is above ground potential or has an AC component with respect to ground.

When powered by the internal battery the 1024 has inherently a very high DC common mode

rejection, but it is not recommended under normal circumstances that 100 V DC common

mode be exceeded.

The AC common mode rejection is determined by the capacitive unbalance to ground of the

output terminals and associated connections.

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