Keithley 7707, User Manual

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Measurement considerations (digital outputs)

The Model 7707 digital outputs provide thermal short circuit protection. That is, when a channel is programmed as an output, 
internal circuitry will be protected from an inadvertent connection up to 1A at 25V.

The protection on the Model 7707 consumes power at approximately 80mA per channel or 320mA per Model 7707 with all 
four channels (11-14; 32-bits) programmed as outputs. Generated heat is dissipated within the Model 7707 module and 
Model 27xx mainframes.

As a result of the power (current) consumption and heat dissipation, adhere to the following guidelines.

Capacity

Model 2700 Multimeter/Data Acquisition System 

— The Model 2700 can provide power, up to a total of 350mA, for both 

module slots. This is sufficient power to properly operate a Model 7707 with any Model 770X module, except the Model 7706 
all-in-one module. The Model 7706 consumes power at approximately 180mA. Power consumption of the Model 7706 is 
independent of digital channels Output State. Therefore, when the Model 7707 is used with the Model 7706, only two Model 
7707 Digital I/O channels can be programmed as outputs (16 bits). Failure to adhere to these limitations will cause erratic 
operations, such as resetting the Model 2700 internal microprocessors. 

Model 2701 Ethernet Multimeter/Data Acquisition System

 — The Model 2701 is basically the same as the Model 2700, 

except it is an ethernet-based system. It does not have a GPIB interface. The limitations stated for the Model 2700 also apply to 
the Model 2701.

Model 2750 Multimeter Switch System 

— The Model 2750 can provide power, up to a total of 1.3A, for the five module 

slots. This is sufficient power for up to four Model 7707s and one other switching module. The capacity limits, when using 
four Model 7707s, are as follows: 

• Four Model 7707s and one Model 770X (except Model 7706) – There is sufficient power to properly operate up to

4 Model 7707s (128 bits) with any Model 770X module, except the Model 7706. 

• Four Model 7707s and one Model 7706 – Four Model 7707s can be used with a Model 7706 but not all digital

channels of the Model 7707 can be used since power for Model 7706 must be factored in. The Model 7706 has two
output channels (16 bits). That leaves 112 bits available for use by the Model 7707s. For example, 14 digital channels
(112 bits) on four Model 7707s can be programmed as outputs. 

NOTE

When a digital channel on the Model 7707 is programmed as an input or off, no power is con-
sumed and capacity limitations do not apply.

Additional measurement uncertainty

On the Model 7707, additional heat is dissipated when the digital channels are programmed as outputs. This heat can cause 
additional uncertainty in thermocouple temperature measurements in the Model 27xx mainframe and 7708 Thermocouple 
Module when more than two digital channels are programmed as outputs. 

The amount of uncertainty is dependent on slot number location of the Model 7707, the amount of time the channel is pro-
grammed as an output, and the other Model 770X module being used. The following table lists additional uncertainty to the 
published specification for the Model 27xx (front terminals), and the Model 7708.   Other modules, such as the Model 7700 
that measures thermocouple temperature, are also affected by this heat, but are still within published specification.