EM D.C. NANOVOLTMETER MODEL N11 Specification.

D.C. NANOVOLTMETER MODEL N31

The EM D.C. Nanovoltmeter model N31 represents a major breakthrough in the field of low level DC voltage measurements. It is the result of years of development in the measurement of very low level DC potential and employs all the experience gained from the EM range of Nanovoltmeters and Picovoltmeters. In addition it has the advantages of analogue output and control with complete isolation, using our new analogue signal and digital control isolator, thus allowing computer control and data manipulation. This isolator operates on optical signals and has extremely high isolation and very high linearity.

Special care has been taken to ensure that the input stage causes the least possible disturbance to the subject being measured and the N31 is designed to operate in sensitive circuits at very low levels. With a little care, it is possible to resolve levels of 100 picovolts, with input impedance which increases to over 1000 M ohm. If the N31 is used in conjunction with a digital voltmeter, 100 pico-volt bits may be displayed with a minimum of flicker. The performance of the input pre-amplifier section gives very high linearity coupled with very low noise and thermal drift and the highly stable gain controlling resistor network gives excellent accuracy.

One of the very important features of the N31 is its ability to measure sources with a wide range of impedance, by following the source 'Johnson' noise characteristic closely from 10 ohms to well over 100K ohm. This means that the N31, while remaining at room temperature, may be used efficiently to measure a source at helium temperature, and even at helium 3 temperature for some measurements. (See the graph of noise voltage against source resistance)

The excellent stability of this instrument makes it ideal for long term drift measurements, and it may be connected to a recorder and left unattended for long periods.

The six position low pass filter gives the operator control over the response time and reduction of noise from the circuit being measured.

A calibrated offset voltage control is provided, with an eleven position multiplier switch, giving a maximum back-off capability of plus and minus one milli-volt. This can be used to measure small changes in comparatively large signals. The level of input which can be offset on any range will be limited only by the resolution of the calibrated potentiometer, i.e. better than 0.01%.

The pure copper input terminals ensure that the very high thermal stability of the input amplifier is maintained, and also that connection to the instrument may be made easily.

There are two outputs at the rear of the instrument, one direct and the other isolated. When extremely high linearity is required, i.e. up to 1ppm the direct output should be used, if possible. The isolator has a linearity of around 10ppm.

The N31 is battery operated from internal chargeable batteries and so has the advantage of complete isolation and the instrument will operate for more than a week on a single charge.

This instrument is engineered to a very high standard and comes complete with a plug on terminal shield.

SPECIFICATION DC NANOVOLTMETER MODEL N31

Click here for graphs : Noise and Impedance Characteristics

Range
Input 1. 12 ranges. +/- 6nV fsd to +/- 2mV fsd
Input 1 to Direct Output. 4 Gain Ranges 1K, 10K, 100K and 1M. Input 2. 12 ranges. +/- 6mV fsd to +/- 2KV fsd (200 volts maximum)

Accuracy
Input 1 to Direct Output Gain. +/- 0.02%. Gain stability 5ppm per deg C.
Isolated Output Remote Controlled Amplifier Gain.+/- 0.1%. Isolated Output +/- 1%. Input 2 +/- 1%
Meter. +/- 1.5%

Resolution
100 picovolts with maximum filter.

Linearity
Direct output better than 1 ppm. Isolated Output Remote Controlled Amplifier Gain. +/- 10ppm. Isolated Output Locally Selected Ranges. +/- 50 ppm. Input 2 to Isolated Output +/- 50 ppm.

Noise
Equivalent noise resistance 10 ohms. Noise voltage depends on filter setting, e.g. filter time constant 10 seconds gives peak to peak noise voltage of approximately 250 picovolts with the input short circuited.

Offset Voltage                                                                                                     Adjustable to zero by a ten turn potentiometer at the front panel. Temperature coefficient better than 300pV per deg C differential or 100pV per deg C for slow change.

Offset Current                                                                                                    Adjustable to zero by a ten turn potentiometer at the front panel. Temperature coefficient better than 3pA per deg C differential or 1pA per deg C for slow change.

Input Impedance
Input 1. Greater than 30 M ohm, 3 seconds after a step input, increasing with time to over 1 G ohm, see input impedance graph.
Input 2. Ranges 6mV to 2V: 1000M ohms. 6V to 2KV: 11M ohms.

Input Level
The N31 will accept input voltage up to +/- 2mV on Input 1.                                            Input levels up to +/- 200V may be measured at Input 2.

Source Resistance
The N31 follows the thermal noise characteristic with source resistance from 10 ohms up more than 100K ohms. With source resistance below 10 ohms the noise in constant down to zero ohms. Above 100K ohms the noise voltage increases over the thermal noise characteristic by 10 dB per decade of source resistance. The input noise characteristic graph shows that if the noise at high and low source resistance are extrapolated as far as the thermal noise at helium temperature, the N31 adds very little to the total noise at 1 K source resistance.

Response Time Constant
The six position filter at the front panel gives a response time constant at the isolated output and the meter which varies from 500 milli-seconds to 12 seconds. The direct amplifier output time constant varies from 100 milli-seconds to 10 seconds depending on the remote gain and filter selection.

Offset
10 turn potentiometer calibrated 0-1000 with eleven position switch giving maximum offsets of plus and minus 100nV, 1uV, 10uV, 100uV, 1mV and a '0' position. Resolution. Better than 0.01%. Accuracy. Better than 0.5%.

Outputs
Direct output is via 4mm sockets at the rear panel and gives gains from input 1 of 1K, 10K, 100K and 1M. The isolated analogue output is on pin 8 of the 9 way D plug and 0v is pin 9.

Isolation
The N31 has an optical isolator for the analogue output and the gain control inputs, giving isolation resistance of 1Tohm. The isolated analogue output has a linearity of 10ppm and a response time of 500 milli-seconds.

Isolated Gain Control
The main amplifier gain may be remotely controlled by applying +3V to the appropriate pin on the D9 connector. Unused inputs must be taken to -3V or be left open circuit. The D9 pin functions are as follows: Pin 1 Filter. Pin 2 Gain 1M. Pin 3 Gain 100K. Pin 4 Gain 10K. Pin 5 Gain 1K. Pin 6 Isolated +3V. Pin 7 Diode Output. Pin 8 DC Output. Pin 9 0v.

Connectors
Input 1 has special EM pure copper low thermal emf terminals. Input 2 and Case have 4mm terminals. Plug on terminal cover provided which fits onto the input 2 and Case terminals. The direct output and case have 4mm sockets at the rear panel. The isolated output and control inputs are accessed via a 9 way D plug at the rear panel.

Meter
105mm mirror scale calibrated 10-0-10, and 3-0-3.

Power Supply
Internal chargeable batteries, giving more than 8 days operation from a full charge. Mains powered charger fully charges the batteries in 24 hours with the instrument switched off or 26 hours when in use. Power required 240V or 110V. 50Hz or 60Hz. 3VA. There is an alternative input to charge the batteries from an external, low noise, current source. Minimum voltage. 18V. Current required 12mA. NB. External charger must be a high impedance current source as the connector is taken directly to the batteries via polarity protection diodes.

Dimensions
Width. 14.2" (360mm)
Depth. 13.4" (340mm)
Height. 6.9" (175mm) Including folded feet.

Weight
22lbs (10Kg)

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Low Level Voltage Measuring Instruments

Low Level DC Voltage Amplifier Modules

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