Racal Instruments 9916 User Manual

4.21 Selection of LF results in a IQ' appearing at IC19q!11. If LKl is in place this
is appl ied to IC1/3 in the Display Assembly, giving an '01\ eights' .display. This
is to provide warning when LF is selected, but the LF Multiplier option is not fitted. When
the option is fitted LKl should be removed.
Frequency Standard
4.22 A 10 MHz standard is required at lC4/5 or a 1 MHz standard at IC4/20. Three
internal oscillator options are available. The specifications ar~ to be found in
the Technical Specification. Model 9442 and model 9421 are ovened oscillators. They are
precision items, and if a fault develops they should be returned to Racal-Dona Instruments
Ltd., or an approved agent for servicing. No parts Iist or circuit information is provided
in this manual.
- 4.23
When oscillator model 9421 is in use a link must be fitted between pins 5 and
6 on the B7G base.
Oscillator Assembly 11-1254
4.24 This is a discrete component crystal controlled oscillator attached to the rear
panel of the instrument. The circuit is shown in Fig. 2. Access to the trimming
capacitor C4 is via an aperture in the rear panel.
Internal Standard Buffer
4.25 The internal standard signal is buffered by Q29 and IC3e. The frequency IS
doubled in the circuit consisting of IC5, \C3d, IC3f, R120 and C80.
External Standard Input
4.26 Provision is made for the use of an external 1 MHz standard, which can be fed
in on SK53 on the rear panel. This signal is buffered by Q16, and applied to
::::4/20 ond to the peak to peak detector C67, D21, 020 and C66. The detector output
>witches on 017 to light LP5, indicating that the external standard is in use.
4.27 It is 0 feature of 1(4 that it wi II automatically change to external standard if an
externa! standard frequency is present. For internal standard ope~ation IC4/20
must be at '0'.
Display System
4.28 The contents of the b.c.d. stores within IC4 are fed in order to the output pins
15, 16, 17 and 18. Each store content is read for 100 }Js, controlled by a 10kHz
.s ignal derived from the freguency standard. The b. c. d. output is ,decoded to 7 segment form
in ICl
of the Display Assembly, and offered to the seven segment numerical indicators in
parallel.
4-4
?916Vol.2

Racal Instruments 9916 Specifications

General

Brand	Racal Instruments
Model	9916
Category	Measuring Instruments
Language	English