SSH-4
User’s Guide
SSH-4
User’s Guide
Revision A - December 1993
Part Number: 85690
New Contact Information
Keithley Instruments, Inc.
28775 Aurora Road
Cleveland, OH 44139
Technical Support: 1-888-KEITHLEY
Monday – Friday 8:00 a.m. to 5:00 p.m (EST)
Fax: (440) 248-6168
Visit our website at http://www.keithley.com
The information contained in this manual is believed to be accurate and reliable. However, the
manufacturer assumes no responsibility for its use; nor for any infringements or patents or other rights
of third parties that may result from its use. No license is granted by implication or otherwise under any
patent rights of the manufacturer.
THE MANUFACTURER SHALL NOT BE LIABLE FOR ANY SPECIAL, INCIDENTAL, OR
CONSEQUENTIAL DAMA GES RELATED TO THE USE OF THIS PR ODUCT. THIS PRODUCT IS
NOT DESIGNED WITH COMPONENTS OF A LEVEL OF RELIABILITY THAT IS SUITED FOR
USE IN LIFE SUPPORT OR CRITICAL APPLICATIONS.
All brand and product names are trademarks or registered trademarks of their respective companies.
© Copyright Keithley Instruments, Inc., 1993.
All rights reserved. Reproduction or adaptation of any part of this documentation beyond that permitted
by Section 117 of the 1976 United States Copyright Act without permission of the Copyright owner is
unlawful.
SSH-4______________________________________________________________________________________________________1
1.0 INTRODUCTION
SSH-4 SIMULTANEOUS SAMPLE & HOLD MODULE
The SSH-4 is a 4-channel, simultaneous sample & hold front-end for use with the PCcompatible DAS-20 and VMEbus-compatible VMECAI-16 and VMEAI-16 analog input
modules. It permits simultaneous sampling of 4 input signals, after which the signals
may be MUXed to the analog board one at a time. The SSH-4 is conÞgured as 4 bipolar,
differentially measured inputs with DIP switch-selectable gains of 1, 10, 100, 200, 300,
500, 600, 700, and 800. Maximum voltage input is ±10 VDC. Output from the SSH-4 is
jumper-selectable as any 4 of 16 single-ended or 4 of 8 differential channels.
Potentiometer adjustments for input and output offset (IOS, OOS) make calibration a
fast, easy procedure. The signal acquisition period may be reconÞgured for your speciÞc
application. Data collection is triggered via a Sample and Hold pulse (TTL) of at least
10 ms duration.
Two 50-pin headers allow easy daisy-chain expansion when more than 4 channels must
be collected simultaneously as well as for connection to the DAS-20, VMEAI-16, or
VMECAI-16 (use cable #CACC-2000). The SSH-4 draws a maximum of 125 mA @ 5 VDC
from the bus supplies. A single DC-to-DC converter for ±15 VDC assures full-scale
coverage of all input ranges.
FEATURES
*4 differential, bipolar analog inputs
*Nine DIP switch-selectable gains
*On-board DC-to-DC converter
*Simple calibration procedure
*Choice of output conÞgurations
*Pin-compatible with DAS-20, VMEAI-16, and VMECAI-16
1.1 SSH-4 Functional Block Diagram
SSH-4______________________________________________________________________________________________________6
4.0 Periodic Calibration/Adjustments
The SSH-4 has been precalibrated and fully tested prior to shipment. However, periodic
readjustment may be required due to component aging, etc. The frequency of adjustment
varies widely depending upon the SSH-4 operating environment. A dust-free, airconditioned, laboratory environment may require SSH-4 adjustment once each year or
two, whereas SSH-4 usage on a shop ßoor or where large temperature gradients are
prevalent may mean more frequent adjustments. A good rule of thumb is Òif you think it
needs adjustment, it probably does.Ó Adjusting the SSH-4 is quite easy with only two
trim pots per channel. It is good to bear in mind that the quality of any measurement is a
direct reßection of the care and precision taken during readjustment.
The two adjustments are Input Offset Adjustment (IOS) and Output Offset Adjustment
(OOS). No special tools or instruments are required. All adjustments should be done
using the gain settings that you would normally use for your application. Adjustments
may be made by monitoring a single channel while turning the relevant trim pot.
4.1 Input Offset and Output Offset Adjustments
1) Set the signal gain to X1.
2) Connect the Ò+Ó, Ò-Ó, and ÒGÓ terminals together for each channels.
3) Monitor each channel via software and adjust the OOS pots for best 0.
4) Set the gain for each channel to what you would normally use.
5) Monitor each channel while turning the IOS pots for best 0 reading.
6) Monitor each channel while turning the OOS pots for best 0.
7) Recheck the IOS (adjust as necessary) for best 0 reading.
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