IET LABS HACS-Z-A-6E-1pF Decade Capacitance System User Manual

IET LABS HACS-Z-A-6E-1pF Decade Capacitance System

Product Information

The HACS-Z-A-6E-1pF Decade Capacitance System is a high-quality instrument designed to meet precise requirements for fixed or adjustable calibration capacitance. It is suitable for various applications that demand accurate and stable capacitance values.
The system features mid-range decades that utilize premium-grade, mechanically stabilized, sealed India ruby mica capacitors. These capacitors are carefully selected for optimal electrical characteristics and low dissipation. They are hermetically sealed to prevent moisture intrusion and minimize drift.
The stability of the capacitors is exceptional, eliminating the need for frequent readjustments during the recommended calibration interval. However, if recalibration becomes necessary, the instrument provides easily accessible trimmer capacitors for the 1 pF, 10 pF, 100 pF, and 1000 pF decades. The other decades can also be calibrated using discrete padder capacitors.
For the lowest decade steps (1 pF and 10 pF), trimmable air capacitors are used. These capacitors are carefully selected for maximum resolution, high mechanical stability, and low dissipation factor.
The system utilizes custom-designed switches that connect four capacitors in a parallel circuit for each decade. These switches are weighted in a 1-2-2-5 code to provide all the necessary combinations for ten equal steps in each decade. Each unused capacitor is completely disconnected from the circuit and has its positive terminal connected to the inner shield for enhanced stability.

Product Usage Instructions

Initial Inspection and Setup
Before using the HACS-Z-A-6E-1pF Decade Capacitance System, perform an initial inspection to ensure there is no visible damage or defects. Set up the system on a stable surface in a clean and dry environment.

Switch Setting
Use the custom-designed switches to select the desired capacitance value for your application. The switches are weighted in a 1-2-2-5 code, allowing for ten equal steps in each decade. Ensure that only the necessary capacitors are connected, and unused capacitors are completely disconnected from the circuit.

Connection to Terminals
Connect the terminals of the HACS-Z-A-6E-1pF Decade Capacitance System to the appropriate terminals or equipment in your setup. Follow the electrical connections and ensure proper polarity if applicable.

Note: For recalibration of the 1 pF, 10 pF, 100 pF, and 1000 pF decades, use the provided trimmer capacitors. For calibration of other decades, discrete padder capacitors may be used.

Chapter 1 INTRODUCTION

General Description
The HACS-Z-A-6E-1pF Decade Capacitance System is capable of meeting exacting requirements for fi xed or adjustable calibration capacitance or any applications requiring precise stable capacitance values.

Unit Features

• Range : 1 pF – 1.111 11 µF
• Low zero-capacitance
• High accuracy
• Excellent stability
• Low temperature coeffi cient
• High voltage rating
• Bench-top or rack-mount operation

Figure 1-1: HACS-Z-B-6E-1pF

1 pF, 10 pF
For these, the lowest decade steps, trimmable air capacitors are used. The capacitors are selected for maximum resolution, high mechanical stability, and low dissipation factor.

100 pF – 0.1 µF decades
These mid-range decades are implemented with the highest grade, mechanically stabilized, sealed India ruby mica capacitors selected for optimum electrical characteristics and low dissipation. They are hermetically sealed to prevent intrusion of moisture and to obtain minimum drift.

Stability
The stability of the capacitors is such that the instrument should not require readjustment for the duration of the recommended calibration interval. Should recalibration become necessary, easily accessible trimmer capacitors are provided for the pF, 10 pF, 100 pF, and 1000 pF decades. The other decades may also be calibrated with discrete padder capacitors.

Switches
Custom-designed switches are used to connect four capacitors in a parallel circuit for each decade. These are weighted in a 1-2-2-5 code to provide all the necessary combinations for ten equal steps for each decade.
The switch circuit is designed such that each unused capacitor is completely disconnected from the rest of the circuit and has its positive terminal connected to the inner shield. See Figure 1-3.
The stability of the switches is assured by the use of large gaps and secure mechanical construction.

Figure 1-2: Capacitance Shunted by Leakage to case

Double Shielded Construction
In order to meet the low residual capacitance requirement, the unit utilizes

• Specially shielded and routed wiring
• The switching scheme described above and shown in Figure 1-3
• A double-shielded construction to keep the zero capacitance at an extremely low level

Figure 1-2 demonstrates the need for the double shielded construction. It shows that a capacitor CHL would be shunted by the series combination of the series combination of the capacitances from the HIGH and LOW terminals to the case. The net capacitance becomes

• CHL + (CHG in series with CLG)

Clearly it would be very diffi cult to get a very low residual or zero capacitance, unless the G terminal is the ground terminal of 3-terminal measurement of the capacitance.
In order to accomplish this, an inner shield is added as conceptually shown in Figure 1-3. It is mechani-cally constructed to shunt away any capacitance between the HIGH and LOW terminals. This inner shield shunts this capacitance when it is electrically connected to the outer shield, forming a 3-terminal capacitor (5-teminal capacitor for units with 10 µF steps or higher). All unused capacitors are shorted to this inner shield at their high ends, and are open at their low ends.
This inner shield is not actually an internal enclosure but rather a cellular structure that optimally separates all conductors and capacitor elements. It also serves to minimize terminal-to-ground capacitance which is necessary when measuring small capacitances with various bridges.

Figure 1-3: HACS-Z Construction

Chapter 2 SPECIFICATIONS

For convenience to the user, the pertinent specifications are given in an Operating Guide, similar to the one shown in Figure 2-2, which is affixed to the case of the instrument.

SPECIFICATIONS

Capacitance

per step

| Total decade

capacitance

| Max voltage| **Accuracy*| Dissipation**

**factor***

| Stability| Capacitor type
---|---|---|---|---|---|---
HACS-Z-1pF Variable

Decade

| 1 pF+| 500 V peak max up to 10 kHz| ±0.1 pF| <0.003 typical| ±(100 ppm + 0.1 pF)

per year

| Air capacitors
1 pF| 10 pF| ± (0.05% + 0.5 pF)| <0.002
10 pF| 100 pF| <0.002
100 pF| 1 nF| Position 1 : <0.002
All others : <0.001| Silvered mica Mechanically stabilized Hermetically sealed
1,000 pF| 0 nF| Position 1 : <0.001
Position 2 : <0.0005
All others : <0.0003
0.01 µF| 100 nF| <0.0003
0.1 µF| 1 µF| <0.0004

• 1 kHz, 3-terminal measurement; series model; 1 Vrms, 23°C; traceable to SI

No zero-subtraction required

• Range
  0 to 1.111 110 µF, in 1 pF steps

• Zero Capacitance
  ≤0.1 pF maximum capacitance obtained with all dials set to zero;

• Temperature Coe fficient
  ≈20 ppm/°C

• Insulation Resistance
  50,000 MΩ

• Operating Temperature Range
  10°C to 40°C

• Shielding
  Double-shielded construction; see below.

• Dimensions

  • Bench : 43.2 cm W x 13.3 cm H x 27.7 cm D (17” x 5.2” x 10.9”)
  • Rack : 48.3 cm W x 13.3 cm H x 27.7 cm D (19” x 5.2” x 10.9”)

• Weight
  8.6 kg (19 lb), for bench version

Connection to Capacitor
Two bnc connectors labeled HI and LO. The shielding is divided into the following parts
The inner shield : minimizes the terminal-to-guard capacitance Outer shield (the case): minimizes the detector input capacitance and noise
The outer shell of the HI connector is connected to the switch shaft. The outer shell of the LO connector is connected to the outer case. To use the HACS-Z as a 3-terminal capacitance substituter with very low zero-capacitance connect these two shields together at the measuring instrument.

DOUBLE SHIELDED CONSTRUCTION
The shielding is divided into two diff erent parts : an inner shield that minimizes the low terminal-to-guard capaci-tance, and an outer shield (the case) that minimizes the detector input capacitance and noise. (See Figure 2-1.)
When these two shields are connected together, the HACS-Z becomes an excellent 3-terminal capacitance substituter with low zero capacitance.

Figure 2-1: Double Shielded Construction

HACS-Z-A HIGH ACCURACY DECADE CAPACITANCE SUBSTITUTER

CONSULT INSTRUCTION MANUAL FOR PROPER INSTRUMENT OPERATION

Accuracy

• ± (0.05% + 0.5 pF) at 1 kHz*
• 1 kHz, 3-terminal measurement; series model; 1 Vrms, 23°C; traceable to SI
• 10 µF steps are measured at 100 Hz

Zero Capacitance

• 0.1 pF maximum capacitance obtained with all dials set to zero
• Operating Temperature Range
• 10°C to 40°C

Shielding
Double-shielded construction

Connection to capacitor
Two bnc connectors labeled HI and LO located on the front. The shielding is divided into the following parts

• The inner shield : minimizes the terminal-to-guard capacitance
• Outer shield (the case) : minimizes the detector input capacitance and noise The outer shells of the HI connectors are connected to the switch shaft.

Capacitance

per step

| Total decade

capacitance

| Max voltage| Stability| Dissipation factor| Temperature

coefficient

| Capacitor type
---|---|---|---|---|---|---
1 pF| 10 pF| 500 V peak max up to 10 kHz| ±(100 ppm + 0.1 pF)

per year

| __

< 0.002

| |
10 pF| 100 pF| 20 ppm/°C| Air capacitors
100 pF| 1 nF| Position 1: <0.002

All others: <0.001

| Silvered mica Mechanically stabilized Hermetically sealed
1,000 pF| 10 nF| Position 1: <0.001

Position 2: <0.0005

All others: <0.0003

0.01 µF| 100 nF| < 0.0003
0.1 µF| 1 µF| < 0.0004
1 µF| 10 µF| 50 V peak max| ±(200 ppm) per year| < 0.0007| -50 ppm/°C| __ Sealed MPPS
10 µF| 100 µF| (Vdc+Vac) < 30 V

or (Vac) < 22 V

| < 0.002

The outer shells of the LO connectors are connected to the outer case. To use the HACS-Z as a 3-terminal capacitance substituter with very low zero- capacitance connect the two shields together at the measuring instrument.

• MODEL: HACS-Z-A-6E-1pF
• SN : H1-1816441

WARNING
Observe all safety rules when working with high voltages or line voltages. Connect the (G) terminal to earth ground in order to maintain the case at a safe voltage. Whenever hazardous voltages (>45 V) are used, take all measures to avoid accidental contact with any live components: a) Use maximum insulation and minimize the use of bare conductors. b) Remove power when adjusting switches. c) Post warning signs and keep personnel safely away.

Chapter 3 OPERATION

Initial Inspection and Setup
This instrument was carefully inspected before shipment. It should be in proper electrical and mechanical order upon receipt.
An OPERATING GUIDE, shown in Figure 2-2, is attached to the case of the instrument to provide ready reference to specifi cations.

Switch Setting
The HACS-Z Precision Capacitor has six capacitance decades. The actual capacitance for each decade is the product of the switch setting and the CAPACITANCE PER STEP indicated below each switch on the front panel.
Note, however, that if any dial is set on 10, a 1 is added to the next decade. For example,
if the dials are set : to 10-9-9-10-1-1, the resultant capacitance is

The zero capacitance of the HACS-Z unit is very low, but all settings are adjusted to accurately provide their nominal values, and it is not necessary to subtract the zero capacitance from any particular setting

Connection to Terminals
In order to properly use the HACS-Z capacitor, it is necessary to understand the use and function of each of the capacitor terminals. Refer to Figure 1-2 and note that a basic capacitor is a 2-terminal capacitor shown as CHL. As described above, CHG and CLG, the capacitances to the case add to the capacitor CHL un-less the 3rd terminal G is connected to the guard of the measuring instrument.
The shielding is divided into two diff erent parts : an inner shield that minimizes the low terminal-to-guard capacitance, and an outer shield (the case) that minimizes the detector input capacitance and noise.
When these two shields are connected together, the HACS-Z becomes an excellent 3-terminal capaci-tance substituter with low zero capacitance.
Using the unit as a 2-terminal capacitor will cause an error of about 100 to 150 pF to be added. This error is not necessarily the same for every setting. This also makes the unit susceptible to noise. However, for high capacitance, the unit may be used as a 2-ter-minal device.

Chapter 4 MAINTENANCE

Preventive Maintenance
Keep the unit in a clean environment. This will help prevent possible contamination.
The HACS-Z is packaged in a closed case, which lim-its the entry of contaminants and dust into the instru-ment. If it is maintained in a clean or air-conditioned environment, cleaning will seldom be required. In a contaminated atmosphere, cleaning may be required.
To clean the front panel, wipe the front panel using alcohol and a lint-free cloth.

Calibration Interval
The recommended calibration interval for the HACS-Z Capacitance Substituter is twelve (12) months. The calibration procedure may be carried out by the user if a calibration capability is available, by IET Labs, or by a certifi ed calibration laboratory.
If the user should choose to perform this procedure, then the considerations below should be observed.

General Considerations
It is important, whenever calibrating the HACS-Z unit, to be very aware of the capabilities and limita-tions of the test instruments used.

Recommended Instruments

• IET Model 1689 Digibridge (direct reading)
• IET Model 1620 or 1621 Precision Capacitance Measurement System (bridge)

The test instruments must be signifi cantly more ac-curate than ±(0.1% + 1.0 pF) for all ranges, allowing for a band of uncertainty of the instrument itself.
It is important to allow both the testing instrument and the HACS-Z to stabilize for a number of hours at the nominal operating temperature of 23OC, and at nominal laboratory conditions of humidity. There should be no temperature gradients across the unit under test.
BNC test terminals should be used to obtain accurate shielded readings.

Calibration Procedure
To calibrate the unit, proceed as follows

1. Determine and employ proper metrological practices.

   • Allow a confi dence band for the uncer-tainty of the measuring instrument and setup.

2. Set test conditions

   • No zero subtraction required At 1 Vrms, series model, 23°C

3. Using 3-terminal measurement confi rm the zero capacitance of the unit is ≤0.1 pF.

4. Determine the allowable upper and lower lim-its for each capacitance setting of each decade based on the specifi ed accuracy.
   For the HACS-Z series, these limits for any capacitance “C” are

   • C±(0.1% + 1.0 pF)

5.  Confi rm that the readings fall within these limits, allowing for the uncertainty band.

6. If any reading falls outside these limits, the associated step(s) may require adjustment (See section 4.5 for details).

Capacitance Adjustment
The various decades are adjustable as follows

Table 4-1: Capacitor type

To adjust 1 pF – 1,000 pF decades, proceed as follows

1. Remove the rear panel; see Figure 4-1. This exposes the trimmers for each de-cade; see Figure 4-2. Figure 4-1: Screws holding the rear panel
2. Adjust each decade in ascending order, starting with the lowest value of the lowest decade.

Figure 4-2: Calibration access holes

To make adjustments

• Set all dials to zero except for the decade in question.
• Set that decade to the value indicated on the trimmer label, in the nominal order of 1-2-4-5 starting with the smallest. When taking a measurement, use a nonmetallic screw driver or tool.

To adjust the 10 nF and 100 nF decades – if technical capability for this process is available – proceed as follows:

1. Loosen the four 10-32 screws holding the cabinet and slide the cabinet off the unit; see Figure 4-3. Figure 4-3: Screws holding the cabinet

2. Locate the particular capacitance of the 1-2-

3. 5 set of the particular decade that needs to be adjusted. See capacitor-labels; see Figure Figure 4-4: 10 nF & 100 nF capacitance sets
   Locate the padder capacitor if installed across the particular capacitor in question.

4.  Adjust the padder up or down by adding or removing a capacitor trimmer.

5. Confi rm calibration.

6. Replace the cabinet.

Replaceable Parts

Table 4-2: Replaceable Parts List

Figure 4-5: Replaceable Parts

Documents / Resources

| IET LABS HACS-Z-A-6E-1pF Decade Capacitance System [pdf] User Manual
HACS-Z-A-6E-1pF Decade Capacitance System, HACS-Z-A-6E-1pF, Decade Capacitance System, Capacitance System
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References

• IET Labs a World Standard In Metrology - Home Page

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