Task Masters for Zero Resistance Ammeter (ZRA) There are a number of options to consider when designing a multiple channel ZRA Task Master.

A: Number of channels required.
B: Ability to monitor couple potential.
C: Multiplexed single ZRA systems.
D: Multiple ZRA system
E: Current Range of each ZRA
F: Electrical Isolation of each ZRA
G: Read Rate

A: Number of Channels Required.

Each channel can monitor a single galvanic couple. Thus in order to monitor 12 individual couples a 12 channel system is required.

B: Ability to Monitor Couple Potential.

With this option a third electrode can be used for each galvanic cell. The potential of the galvanic couple is measured with respect to this third electrode to give the couple potential. 

C: Multiplexed Single ZRA.

In this case the instrumentation uses just a single Zero Resistance Ammeter (ZRA). The ZRA is switched from channel to channel as the measurements are made in turn. The technique is particularly cost effective if a wide current range is required for operating many channels as only one complex multiple range ZRA needs to be used. The downside of a switched system is that the galvanic couple is not permanently connected to a ZRA. Thus the galvanic couple receives a slight electrical kick every time a channel is switched into the ZRA for monitoring purposes. These electrical kicks are not desirable and tend to lead to a slower repetition rate as a settling time is often required before measurement.

D: Multiple ZRA system.

An excellent cost effective choice if the current range required is not excessive. Each galvanic couple remains coupled to a ZRA at all times.  Hence electrical kicks as experienced with a switched sequential system are not a problem. Thus a much faster read rate can be used without the need for settling time as with a switched system.

E: Current Range of Each ZRA

A typical single range ZRA will give a comfortable current range over four decades. Current ranges up to 7mA are the most cost effective. Each ZRA can have a wider range of current using switched current ranges.

F: Electrical Isolation of each ZRA

Electrical isolation enables each ZRA and thus its associated galvanic couple to be electrically isolated from the other channels. With electrical isolation several galvanic couples can be placed in the same cell at the same time without externally imposed interference between couples. Multiple channel switched ZRA systems also offer isolation between channels.

G: Read Rate:

Typically the maximum read rate for a Task Master is approximately one reading of each channel per minute. However if required the read rate per channel can be increased to 50 readings per second on all channels at the same time. The practical limit to the number of channels reading at 50 readings per second is 32.  However this can be increased if required. 

Examples of ZRA based Task Masters.

Isolated 30: A thirty channel system with a ZRA per channel. Each channel has electrical isolation twin current ranges and the ability to monitor the couple potential. Fitted with gold plated Lemo connectors and 5 meters of electrode cable.

Galvo Gill: A twelve channel system with a ZRA per channel. Each channel has four ranges and the ability to monitor the couple potential. The Galvo Gill is typically supplied without electrode cables but fitted with 4mm sockets for ease of connection.

Due to the great variety of these types of instrument we have not supplied pricing information. Please decide what you want using the above information as a guide and ask ACM Instruments for a quotation. Alternatively contact us by 'phone and we can ask you the necessary questions and quote to your specifications.